A few questions

Hi again, not sure where this goes, so:

1) How often does my PC, by default, create a system restore? Should I create my own, or not really unless I'm about to install some dodgy program?

2) Disk cleanup and disk defragments - are they a good idea to do around once a month? Can they mess up the PC? How long should a disk defrag take?

Many thanks for the (anticipated) help.