What is the point of 3 and 4 ply toilet paper?

While shopping today I noticed that toilet paper now comes in 2, 3 and 4 ply. I think I have been buying 2 ply but I prefer the triple length rolls so I don’t have to buy as frequently and now they only come in 3 ply. I wonder if it is so people use less? Do you use less if it is 3 or 4 ply? I know, not an earth shattering subject, but I do wonder???