I personally have found System Restore to occasionally save my @ss when something gets messed up -- and am too lazy to keep turning it on and off -- so I set it to use 3% of my SSD (about 1.79GB). It seems to be an acceptable compromise. By default, Windows sets a much larger % of disk space, but then you just end up with lots of old restore points.
i3-3225, 3.3GHz w/stock HSF, GigaByte H77M-D3H
2 x 2GB + 2 x 4GB Kingston RAM = 12GB, no discrete graphic card (just IGP HD4000)
Samsung 840 EVO 250GB SSD | Intel 520 120GB SSD | 1TB WD Green HDD
Silverstone Temjin TJ-08E case | CoolerMaster eXtreme Power Plus 460W PSU
Dell U2312HM 23" LCD | Samsung 171N 17" LCD | Windows 8.1 Pro 64-bit
Location: Thailand (several hours south of Bangkok)