Maybe you don't technically "need" a starter with dry yeast but I think you gain a bunch doing a starter, most importantly the lag time until discernible fermentation begins is greatly reduced. You are pitching what was dormant yeast but which now is fully active, and you're pitching orders of magnitude more yeast cells than you would simply sprinkling the dry yeast in the fermenter, which I would guess is interesting if you use carboys. I have only used liquid yeast a few times, and it does take off faster than dry yeast does when you are getting your starter going, but once pitched in the wort, in my limited experience an appropriate starter takes off much faster.
FWIW, I found a 30-some year old packet of Edme beer yeast [not lager yeast or ale yeast, just "beer" yeast] a while back, and not being the sort who can stand wastefulness, I was wondering what to do with it. I wasn't about to risk a batch of beer on it, so I used it for a batch of Treberbrot burger buns - best damn bread yeast I have ever used, and I've been baking bread for more than 40 years!