Definitely check for an over-long case with every loading. If trim is required, do it.
I know a guy who had been reloading a few years. Came to me because I've been reloading since 1971. He was having trouble closing the bolt on his .308 rifle. A load he'd worked up to safely was now exhibiting signs of high-pressure.
But what bugged him most was the difficulty of closing the bolt on a round.
When I asked him how often he trimmed his cases, his reply was classic, "You have to do that every time?"
He'd reloaded 3 or 4 times without trimming. He'd never trimmed before, though he had the tools to do so.
Trimming is very important. I wish more emphasis were placed on it by reloaders.