why erase hard drive

[tim100]

is there any reason to erase hard drive and do a new install other than selling mac or new os?

 

[aeboi]

is there any reason to erase hard drive and do a new install other than selling mac or new os?

removes useless junk that ultimately builds up on an old hard drive
just bits and pieces from programs and whatnot

 

[tim100]

removes useless junk that ultimately builds up on an old hard drive
just bits and pieces from programs and whatnot

when should it be done?

 

[aeboi]

when should it be done?

It's not really something that you should do if you don't have any slowdown problems. Use a program like cleanmymac, they essentially perform the same task.