“Set anything” under the bindings is to allow you to use the ‘+’ / ‘-’ method of adjustment.
An example would be as in FSX you could use the keyboard to change mixture on engine 2 only by…
press ‘m’ - press ‘2’ - press + or - as required to set the mixture. In your case, if you bind ‘t’ to the “set trim” command, you could then press ‘t’ - press + or - to adjust. Of course, for that to work you would also have to bind the “cockpit interaction - increase” and “cockpit interaction - decrease” to the + and minus keys first.
These settings are more used for interfacing custom cockpit controllers and are of less use for general control. They are especially handy when using rotary encoders.
I have mucked with some of them and the implementation is a bit hit and miss at this point. Maybe as the SDK moves forward more of them will become active or operate as expected.