To me, it all depends on your situation.
Most of the guns I've acquired were bought after giving careful consideration to the decision.
Perhaps because of that, I've almost always later regretted getting rid of a gun. I avoid getting
rid of them because of that now. I'm not in the position of needing to sell something before I can
buy something else that I currently want. (Within reason - not talking about vintage side-by-side shotguns or Single Action Armys. Those are outta my price range.)
On the other hand, if your guns/ammo/reloading budget is at its max target and you really need
to get rid of something you don't use to stay in budget - the answer is more obvious.