some programs will ask for HUGE ammounts of memory on startup (whether they need it or not) On request windows will allocate these programs their desired ammount of memory from your pagefile.
Disable your pagefile and you may find yourself running out of memory pretty quick also even if you have plenty your performance can drop quite dramatically. Ive also had some DEP errors thrown up on systems with no pagefile , programs just wont start , DEP blocks them as they start using memory thier not allocated , turn PF back on and all is well
Leave the pagefile and leave it at system managed