It will give you more options in playing with his foreskin. Uncut foreskin is much more sensitive. If he has a lot of precum, it serves as a holding place - which could be phenomenally pleasurable for both.
In general, it will take less huffing and puffing to get him to orgasm. Depending on your/his intentions, act accordingly.
It will be like he is cut only more skin. Really, don't over think it.