Considering a win in game 3 basically puts us in the finals I'd say VERY crucial. Considering we need to be well rested to beat the Lakers in the finals and they appear to be headed for a short series as well, I'd say VERY crucial. Can we win in game 4 and then win it in 5 or 6, yes. For title purposes we need to win them both and get some rest.
If your only concern is rest, then it's actually not very crucial at all. If this series and the WCF series go 5 or less games, we'll get at least 6 days off (Finals would start on June 1st). If our series goes 6 or more games, then we're looking at either 3 or 5 days rest depending on whether it goes 6 or 7 games (the Finals would then start on June 3rd). So, really, we're looking at anywhere from 3 to 8 days of rest, that is, if we advance. Assuming we remain healthy (and don't need days off to get healthier), I'd rather we're closer to 3 days rest than 8 days rest, everything else being equal.
While I'd welcome a sweep (who wouldn't?), the extra rest isn't the reason why. We're 0-2 right now in the games in which we had 3 or more days off, so long term rest seems to have some negative effect on this team. We'll see tonight if we can turn around our rest=defeat formula.