Higher is typically not a problem.
The real issue is when you’re flying a small GA, entered a flight plan for 8000 ft, and it suddenly tells you to climb to FL240 when you’re 10 miles from your destination. You can request a lower altitude (like the 8000 feet you’re currently at), but it will expect you to first climb to the designated altitude before it will allow you to fly at the altitude you’re currently flying at. And obviously, if you’re flying a C172, that FL240 isn’t going to happen. Nothing left to do at that point but cancel IFR and finish off your flight VFR instead.
ATC has some serious issues.