Keyboard Maestro keeps a clipboard history, so if you have large numbers of large clipboards, it can mount up quite a lot.
There are preferences described in the Documentation that can limit the clipboard size, such as:
You can set the maximum number of items in the clipboard history (default 200)
defaults write com.stairways.keyboardmaestro.engine MaxClipboardHistory -int 200
You can set the maximum clipboard flavor size (default 100MB)
defaults write com.stairways.keyboardmaestro.engine ClipboardFlavorMaximumSize -int 100000000