I'm very flexible, but have never been able to fully do the splits. It's never affected anything other than my pride when my siblings could all do them.
I can't do the side splits, but I can to them front and back. It really hasn't affected our sex life too much, but it's nice to be able to go into some tricky positions. My fave is doggy style, and I pull my leg behind me, with my foot by my head.