Hi Marianne,
Good question, and really not too complicated.
Dry cutting gives a stylist a better visual on the finished look, you can see how your shaping looks as you go...It doesn't work* better * on one hair type (curly or straight) I use this on both (I only dry cut my stick straight hair)
Most clients who have alot of inconsistencies in how their hair dries is the *crucial* element here, and determines weather I will dry cut or not.
Simply put...if your hair tends to shrink a TON, or due to cowlicks etc. it dries uneven...even if it is cut perfectly even...dry cutting is in order.
Some other factors involved, but you get the idea:)
Some stylists have turned this into a bit of a gimmick by specializing in dry cuts only...don't buy into it...both wet and dry cuts have their place:)
