Well, its up to your judgement but the following rules do apply.
[ul][li]everthing you wont need for any animation or modelling purpese is to be deleted. What this means is that you can delete the history:
- While modelling once you know you wont go back on your modell, or whan you have one convinient logical part done. and you notice your modell has become bloated.
- before you start making animation bindngs! that is not to sey you cant use modelling history as animation parameters so if you do only delete what you dont need! Designing beforehand is important an 50%-75% of the job!
[/li][li]Dont delete if you wont have to... But its a big performance boost.
[/li][li]Dont delete history whan you have custom connections unless you know what you are doing (if you do the connections then its asumed you do know what you are doing!)
[/li][li]anything you dont need! what you need depends on what you are doing offcourse!
[/li][/ul]
also having one file with all history intact is a good idea! if possible... for poly modelling it often isnt!