Party Poker Pre-Flop raise

[jmcfg8]

What is the value of raising pre-flop in the partypoker single table tournaments? I don't usually raise until late in the tourney unless I have KK, AA, and occassionally AKs or QQ. My problem w/ raising pre-flop on here is the fact you get so few chips to begin with. Any raise to get out trash hands puts a dent in 800 chips. If you miss the flop its so costly to chase a hand or try and call a bluff. Late in the tournies where stealing blinds is invaluable I raise much more. My question is: How do you handle pre-flop raising on partypoker in the early to middle stages of a tourney? Do you do it often, rarely; if so, why? Thank you