When I played online, I took notes constantly. Like all the time. Also used a label system based on categorizing preflop states.
On GGPoker specifically, I mean, it only remembers session stats, so it's your job to write down session stats and convert them into lifetype stats for the opponent. If someone has played 105
hands, write a note that says
20/13/8/35 (105)
And if they already have a note like that and it ends with (180), then combine them into a single note that ends with (285). You will require basic arithmetic
Rake in online cash games is brutal so you should chase every edge you can get. If you're playing MTTs, then eh, way less impactful, I guess you can not bother unless someone does something wild.