I had a lip piercing for about 5 years. Took it out a few years ago cos
1. getting bored of it, and my life was changing a lot
2. sick of seeing little kids running about with the same piercing thinking they were cool.
Have it wherever in your lip you want. If you care about what others think, some locations look better than others. It also suits some faces better than others. If you have a thick bottom lip, then a ball under the centre can look good, but check it's in proportion to your lip and general face.
Make sure it's with a pro piercer, someone who is well respected in the piercing community, and listen to their advice regarding aesthetics and hygiene. Visit the studio for a chat first, and if you feel uncomfortable or pressured, or if you see any dirt, don't use that studio.
I have no scar whatsoever. However, a little bit of my gumline is receded a couple of mm down one front tooth cos of the end of the labret bar (socket that holds the ball) was rubbing on it for 5 years. My dentist says its not a big deal and he can fix it, but I haven't been bothered to do it, as it's never visible. If it was visible, I would be annoyed and possibly regret it.
You can take out lip piercings whenever you like for job interviews, meeting granny etc. Some people will say they close up if you take it out for more than a few mins. That's bollocks. Leaving it out overnight is possible, tho the hole will shrink, and you'll need a thinner gauge to insert in the morning.
Some rings and labrets are more comfortable than others. Some were agony for me to wear after a few days, but swapping to a different labret bar, with a base a few mm wider made a huge difference.
Hope that helps.
