When will Finder use large amount of memory?
Solution 1:
I can't say much about preventing this, but there is no need to reboot. Just kill Finder, using Force Quit from the apple menu or killall Finder in a Terminal window. A new Finder will then be started in the old one's place.
Solution 2:
This inconvenience is caused by a finder prefs entry:
"show in new window: all my files" this is consuming too much mem. Select a different folder and all is fine
Solution 3:
Removing 1k screenshots and images from the desktop reduced Finder's RAM usage from 1.5G+ to 220 MB instantly without relaunch.