Relevant quote from Wendler just yesterday:
"Best book on training ever written: your training log.
If you don’t keep a detailed, written training log, you are wrong. I can’t tell you how important this is for success. Simply put, if you don’t keep one, you just don’t give a shit."
You’re a trainer, no? (I’m pretty sure, but am having an ironically timed brain fart). Juggling clients’ sessions and worknotes always seemed to interfere with trying to commit my own stuff to memory. Wasn’t worth getting anything scrambled, so I always kept a log.
To be fair though, I rarely review old logs once they’re done. I record the day’s session as it happens and refer back to the last time something like that session was done (for weight/rep PRs, etc.), but I hardly ever flip through old logs to track down patterns like assistance exercises that work well.