I can’t think of any disadvantage using a lined fretless bass until You’re blind, in that case You could possibly save few bucks by buying unlined…
I have owned several fretlesses, always lined. I’ve played them hundreds of live, theatre and studio gigs so I pretty well know sometimes those lines can be real life savers. I`ve never ponytailed my hair but it was very long indeed something like 40 years ago and didn`t always wear a suit. Here is the fretless I use these days, lovely Sadowsky N.Y.C. modern 5 wich I ordered lined, of course. I wish very Happy New Year to all of You basschatters!