It will be like he is cut only more skin. Really, don't over think it.
In general, it will take less huffing and puffing to get him to orgasm. Depending on your/his intentions, act accordingly.
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.