no it doesnt, well atleast i have not noticed any difference in my battery life with / without SBS, allthough, little things like BT and WL turned on do, if you go out, flick them off in SBS, well, i do atleast, cause my battery sucks. haha.
The native mutli-tasking doesn't 'cause it pauses app's in memory (as far as i know, either that or its snapshots) SBSettings doesn't use much at all, i install it on all my iDevices and suggest it to friends.. its probably uses less battery than going to settings and then wifi and then flicking to off!
On the contrary. SBSettings helps increase battery life. With the correct toggles and even using SBSchedule, you can make your battery last a VERY long time. I have mine schedule to turn things off at certain times. I go to bed with my i4 unplugged at about 50% battery and wake up 8 hours later and it is dropped to only about 48%. Using the toggles is a smart thing to do when you need to preserve battery.
I haven't ever noticed a difference. Probably because I have never had a phone that didn't have it on there. There is an age old thread on this forum that discusses this topic.