There is some question as to how much of that bacteria survives in bags. I bought Ocean Direct Livesand and verified the presence of micro-organisms with a microscope. I can't say how long it was in a bag before shipping, but upon shipping, the livesand remained bagged for about a week before opening. I can not speak for other brands. I do like that brand's substrate. However, many hobbyists consider such livesand a waste of money, since similar bacterial populations can be achieved simply with liverock and patience.
My own anecdotal evidence would suggest livesand to be somewhat beneficial. My 37g with 5" DSB (all of it livesand) is a little over 2 months old, but has shown considerable biological robustness from an early stage. Everyone seems to think my tank should be overgrown with green algae and my nitrates thru the roof, but it's not. Algae growth is very under control, nitrates have yet to reach testable levels, my Tunze Nano skimmer won't even make brown water from time to time it has been so clean. I run a 250w-MH for 12 hours a day, 2x24w-T5-blue for 24/7, and only have 40lbs of liverock in what is actually a 50g system. Everything looks great, and I'm inclined to believe the generous use of livesand has something to do with it. My results seem a little difficult to justify otherwise.