Good write up on the github page explaining why I would bother with it, the short version included:

In Wayland, whatever app you copied something from is the one actually holding onto that clipboard content, the compositor itself doesn't store it. This means if you close that app, whatever you copied disappears too. swayclip fixes this by keeping its own copy of your clipboard history, and only steps in to "hold" the clipboard once the original app closes or exits.