I always do a clean install. It can be a chore, but perhaps that's why I never have any problems.
I've never done a clean install. My system has a lineage straight back to my first install of OS X, but I do know how to weed out junk from my Libraries folder and find pockets of hidden storage. I prefer to pull out the weeds than to re-sod the whole lawn. I have lots of legacy software licenses and starting over is just both too risky and time consuming.
I've managed to remove around 200GB of kruft from my 2TB drive that wasn't doing me any good over the past couple of years.