Help needed with m' diffs

[Team No Idea]

Hi all, I've just replaced the whole front diff in my B44 today as it was getting rough, which leads me to a novice's question..... how often should i be stripping and re-building my diffs??
Should i wait until they start to feel rough or would i be best stripping, cleaning and rebuilding frequently?, once a month or something....... the car is mainly used every wednesday night indoors on slippery wooden floors.

Also being fairly new to all this what exactly do the shims in the diff do??