I'll just get right to it: pretty much no. Sephora's spring sale is happening right now, and they're offering discounts from 10%-15%. VIB Rouge gets 15% off and a little longer to use the discount, VIB gets 15% off, and BI gets 10% off. Those are some dinky fucking discounts, and if you don't have a least a BI account (which is free), you get nothing.
Unless you buy a ton of stuff, 10-15% is not going to add up to much saving. And if you're buying a lot just to make the discount larger, that doesn't make a lot of sense.
I think it's only worth shopping during this sale if there's something you can't get on sale anywhere else, ever. For instance, brands like Tarte, Too Faced, Urban Decay, and many others have a couple of 20-30% off sales each year. Chances are that you can wait for one of those if there's something from one of those brands on your list. (Note that when I say "you." I really mean "me." That is as much an anti-haul post for myself as for anyone else.) Those brands often offer free shipping too, or you can get it by signing up for their loyalty programs, like the Urban Decay Beauty Junkies thing. (Tarte is on Hautelook right now, in fact, so you might do better there, although you'll have to pay for shipping.)
If you can't get free shipping during one of those sales, but you have a Sephora Flash membership, and you only want one or two things, maybe 10% off plus free shipping will be a better deal than 20% off plus shipping charges. That is a reasonable calculation to make. Or maybe something has already been marked down in the sale section and you want to get a little bit more off the price before it sells out. Sure. (By the way, I bought the Chic It Easy set back in January, and it's pretty great. Even though it includes a tinted moisturizer and concealer that will only work for certain people. You get a full-size Nars Jungle Red lipstick in there, which is normally $28, while this whole kit is on sale for $25.) Or maybe you need something RIGHT NOW, so 10% off is better than nothing. (Do you really, though?)
In general, I have a pretty hard time mustering up enthusiasm for sales that offer less than 25% off. How about you?