Keep copies of player character sheets
Having an up to date copy of a character sheet gives you a lot of power at the table. If you need to secretly roll an ability score check for a character, you don't need to ask the player for the information. If you require that player's tell you all changes to their statistics, it's easy enough to maintain. Also, if a player forgets or loses their character sheet one week, you can keep them in the game.
Away from the table, the sheets are still useful. The character sheet collects a player's hopes and goals. When you're planning for future sessions, read over your player's character sheets. Is there a carefully tuned combat monster? That player is probably looking for exciting and challenging fights. Has someone maximized the diplomancy skill? They'll be frustrated if they never get to shine in that way. It's also a useful source of plot ideas. Do they have the character flaw "Dependent: kid brother?" Time to write the kid in.