I'm probably in the odd minority,but if it's my songs,I seldom work on more than one thing at a time and I bash it until I get some kind of a result. I don't think I have ever had an unfinished track,just some projects take more time to finish than others. I
do have plenty of tracks sitting on 'private' though,so maybe that's a thing.
Having said that,I had one going a couple of weeks ago,then I realised I had plagiarised one of my own songs and the whole structure was too close to ever hide the fact,so for the first time I binned the lot! The damn thing was nearly finished.
Maybe I'm not as picky as some,but there is very little that can't be salvaged in some way,it's just some will be better songs than others.