LOL i love it for various reasons
1) Cumming while she keep on sucking and all is extremely good sensation wise, but the girl need to have an excellent thecnique, so she make me cum. Thing i realize i got much more sensation in the pre-sex BJ than the post-sex one. So if i opt only for a BBJ i could do it easier, but i also apreciate to have sex with her, especially if its a first time.
2) The concept of a CIM/COF is arousing by itself as a sexual act. Maybe its my porno background(growing up with it)... who know, i like doing it. When i watched porno for the first time the guy gave a big fat juicy COF to the actress and i was like "oh shit !" and since i watched porno before having sex for the first time, i always wanted to finish it this way. It arrive often i pay the extra and i end up jerking myself in the girl mouth, but i still enjoy it very well, and i like when im done cuming they suck on it some more. Some girls tend to run to the bathroom too fast... I guess i should mention it before lol.
3) I can't cum in a rubber... I never experienced really sex without it, exept on rare accidents where it got away but it was not really long before we realize it. But one thing for sure i could never cum in sex... no matter how hard i try. Maybe its a mental thing as i would feel i "lost" a good load lol, i dunno... If CIM/COF is not a possibility , usually COB is.. so i opt for that, wich is still better to me seeing a nice pair of big boobs with cum all over them, then having my good load in a rubber... I would even do a Cum on Ass/lower back before cumming in a rubber.
I sometimes make jokes about the fact i could keep pounding a girl for hours without ever loosing it lol.