Once piercings start to show the first sign of rejection - they should be removed immediately.
People leave them to "see what happens" and thats how they end up going all pussed up and minging and you end up with loads of scar tissue - then they go for another piercing before its healed properly (which incidenally takes about 18 months overall) then that rejects again and so we have a vicious cirle and folk end up being scarred.
I had my belly done in 3 places (one at the top 2 on the bottom) the top one was fine, but the bottom ones rejected - i took them out at the first signs and all i have is a teeny mark where the holes were.
Scarring IS unavoidable, but folk often dont know what to do when a piercing rejects and so they end up with an unsightly scar.