I think some people are using the term incorrectly. The internal anal sphincter is RIGHT NEXT TO the external anal sphincter. So obviously if you go through one you are almost immediately going through the other. So that's not the internal sphincter we are talking about.
One of my favorite fuck buddies is a nurse, and I'm one of his favorite tops because he tells me I am one of the few who can reliably go through his "second hole." By that he means long enough to come out the other end of his rectum into the sigmoid colon. At that point there is a narrowing* between the two sections which both partners can feel during fucking. For the top, it feels great because I'm balls deep inside him and yet the head of my cock is going in and out of a hole, which is the best sensation for the head. Hence the huge attraction for the fucker. I'm sure it feels good to the fuckee also, but someone else will need to describe that.
If you're longer than your partner's rectum, you are both in for a very good time if you take the time to find the right angle to go through their "second hole." INCREDIBLE sensation.
*I'm not sure if that's technically a sphincter or not. Someone with more medical training than I have (which is basically just fucking doctors and nurses) or the time to research it will have to answer that.