It won't increase your volume(well they can but I assume you don't want to be deaf)but will it make your headphones sound better maybe. If you buy much better headphones and a great headphone amp, sure it might sound better but plan on spending a lot of money.
My friend and I had the same question as you have and we even had an argument about that issue and in the end we have found the unequivocal answer.
So let me tell you that you can save your money and spend it on other things if "making your sound be better" is your issue, because we searched and found out and even checked by our own and amp can only increase you volume and your volume only
hope I have helped and you won't do any mistake
Listen to thee_prisoner, Jastin and Bobby... they have told you already the answer why do you keep asking ?
I have a computers lab on New York, one of the most popular in the city and as a person who deals with those kind of things every day (amp also of curse) I can tell you one and for once that amp should (and its only purpose) is to increase your volume...
hope you got it and won't ask for more comments because you got enough...