You are probably not interested in the plot development or the foreplay, perhaps you just want to get to the time mark where one of the gays is getting his ass fucked from behind.
This is the common case for gay porn viewers because obviously gay sex can get routine-ish, it is all about the cock and anal sex-you just know how it is going to end. Porn viewers sometimes get tired of watching an entire video of a porno, it is either the plot is boring and repetitive and there is nothing new to it, or that you are really horny that you do not really want to spend an hour or two to sit through an entire sex movie and just get to the best part quick and get off.