We’ve been anal-only off and on for a while now. I can’t say how long exactly, but long enough–I think–that any averse affects would have manifested themselves in some form or another by now. My ass isn’t looser; however, I have noticed the muscles there relax easier now, so penetration is less difficult and more pleasurable for me. My husband says its like making love to a woman who knows how to pleasure a man, vis-a-vis using muscle contractions, so I can only assume that means it doesn’t feel ‘looser’ for him. I can’t recommend anal-only enough. If you can get past the initial discomfort, the orgasms are far superior to anything you’ll get from vaginal sex alone, and the intimacy can’t be beat.