Salt Blocks for Guinea Pigs?

Yesterday at Petco, I was buying some guinea food and fluff when I stumbled upon "salt blocks". They looked interesting and came in some tasty flavors. But, I was unsure as to whether guinea pigs needed salt blocks-- I had never heard anything about them. Up to this point, I've just been giving him a good assortment of pellets, hay, vitamin C treats, and fresh veggies like red peppers, cucumbers and parsley. Petco didn't have Guinness' favorite vitamin C orange slice treats in stock, so I just bought the pellets and fluff and went home. 

Then, last night I was exploring some info about guineas on the PETA website (they don't have a very comprehensive info section, but just the basics) and it mentioned something about salt blocks. This intrigued me, since I have read just about every single website and book about guinea pigs, and never heard anything about salt blocks. 

It makes some sense that they need more salt, since it doesn't seem like they get much in their diets. Guinness has also been drinking water like crazy lately, so I was thinking maybe he needs more salt to retain water.

Today I read some things on guinea pig discussion website, and people said salt blocks are unnecessary. One person even said it can hurt them by causing kidney/bladder stones. I'm not really sure what to think!

Oh well, if anyone has any info about these salt blocks, let me know. I will probably buy some and see how Guinness likes them. If it looks like he's eating too much of it, I'll take it away. I'll update soon!