I used to constantly use elevator trim when flying to maintain level flight in both these aircraft.
Then I learned that “throttle controls altitude”, and now I almost never trim at all. I just adjust my throttle to adjust and maintain level flight.
The only time I have used trim since learning this is a recent flight where my plane iced over so bad I needed to adjust elevator trim to keep from descending at max throttle.
What other scenarios do you find you need to use elevator trim in?
You will still use trim to keep the two variables in place… speed and altitude or attitude.
That’s right in certain situations. But first of all you control altitude with pitch and power.
For a Leveled flight it could, no it is necessary, that you trim your yoke forces away.
Why is it so?
I.e. you fly with 75% Power a leveled flight, and want to fly faster. You push the engine to 85% and what happens? Your nose rise up to to the air and all the additional power is going into a climb. That’s not what you want, so you push the yoke to maintain your flight level and increase the speed. And now you need to hold the yoke in that position…no…you don’t, because you begin to trim that force away and now the plane hold the altitude with the higher powerlevel or better higher speed without touching your flight control.
That’s just one of the situation where you need trim. In fact, trim is used the whole time you fly, doesn’t matter if you are do the work, or the AP, if you fly a C152 or a B747.
I can think of a few…
Other than that, you are correct, you don’t need trim.
There are target throttle settings and airspeeds the aircraft is happiest at. The design of those two aircraft in particular includes little trim tabs on the control surfaces that are bent in just such a way as to put the aircraft in stable, straight/level flight when the throttle is set at the right RPM for each given flight condition.
When you are climbing you should be setting the throttle to full and put the aircraft in the pitch attitude the achieves either best rate of climb speed or best angle of climb speed, depending on the situation, then TRIM to relieve control pressure to maintain that.
If you are flying properly, you should be making a trim adjustment EVERY time you change attitude.
Interesting!
I had assumed that max throttle + neutral trim would achieve the most “comfortable”/“most efficient” climb rate for the aircraft.
What are good references to know what the actual “most efficient” climb rate is for these aircraft if that’s not the case?
The Cessna Pilot Operating Handbooks are readily available online.
Well, in that sim is not really necessary to know anything, but it makes life or sim reality easier if you read the manuals.
I’m really getting into the weeds now after months of flying and constantly learning.
I’ll definitely check out the manuals now.
FYI, if you are flying a 152/172 and start to “Ice over”, you NEED to descend. Get OUT of the icing conditions. Those aircraft are NOT certified for flight into known icing conditions (FIKIC). You must get to warmer air, or at the very least get out of the visible moisture, ie:clouds.
Try this in the TBM930 and you will hear the Stall warning much more than you can bear. 
Oh, I know!
On that flight I actually ended up landing on a dirt road and sat there for 15 mins to let the ice melt 
Trim should always be used. Use it control your airspeed (throttle up then trim nose down to maintain altitude or vertical speed)
Power does dictate whether you climb, cruise, or descend for a given pitch. Setting a pitch angle will ultimately dictate your airspeed. In order to maintain that pitch angle you will have either forward or aft yoke/stick pressure and trim is used to relieve that pressure. You should always be trimming.
You climb typically at the best rate of climb speed (Vy) and full power. You cruise at a given altitude and at a given cruise power setting. You descend at various descent speeds and at a set power setting. In order to do all of the above, trimming is always needed.
Excellent answers guys, this is exactly why I’m on this forum 
You don‘t use trim to maintain a pitch (or vs) but you use your controls. That‘s what they are for.
Trim is used to release pressure (force) from your controls. If you constantly have to push then trim forward until the pressure is zero.
In level flight with small aircraft you use the throttle for very fine adjustments as the airplane will want to hold its speed. But first you trim it properly. If you have a rudder trim you‘ll learn the lesson quickly: every power change requires you to adjust the rudder trim. If you don‘t have it you either now the power setting where you can relieve the pedals or you will have to put pressure on one leg.
Throttle for descent and pitch for speed is something else. It‘s a basic understanding in single engine airplanes because altitude is speed and speed is life. If you fly without engine you regulate your speed with your nose only and you use this concept on light aircraft for safety reasons. But practically pitch and throttle go hand in hand. In heavier and sluggisher aircraft you‘ll use throttle/thrust for speed.
I can hear my old instructor bellowing at me now. Power…Attitude…Trim!
At any point he’d shout…I have control!..Testing to see if the aircraft (Chipmunk T10) was in fact trimmed. Enough thumps on the back of your flying helmet reinforces the drill.
The British Army taught flying just like drill, lots of shouting.
As someone who has spent a lot of time flying day and night at the margin of VMC and IMC (police single pilot), you find it’s far easier to have thinking time when you’re not struggling with an aircraft that is trying to get away from you all the time because it’s out of trim.
Fly the training missions!!!
With AP off, all the time
If you’re flying a real plane, your arms will get fatigued if you don’t use trim! Also more difficult to maintain a stabilized takeoff / landing at the proper speeds.
Scott
Cruise speed of Cessna 172 is ~ 110 kts ground speed.
Descend on upwind approach at 90 kts.
50 kts over the skirt.
Have a go at flying between two provincial fields to a time schedule. Based on 110 kts cruise.