Default Question choosing the carrier when flashing rom

Can anyone tell me if it matters on choosing a carrier or leaving it set to international when flashing a new rom? Example, a rom may only list international and another will have all of the carriers to choose from. I am on T-Mobile and the only difference I can find when I played around with it was that by choosing T-Mobile I ended up with T-Mobile specific apps whereas I didn't see them on the international. What I don't know is if choosing international instead of T-Mobile will affect signal, data, ect. I guess it shouldn't affect anything if not all of them have the choice for all carriers in flashing but I was wanting to know any technical specifics on this. Thank you.