I'm in the process of moving photos out of my iCloud Photos account and onto an external hard drive. Thanks everyone for the tip!
This is still a little puzzling, though.
In iCloud, I probably have about 400GB of photos. When I go to the Settings>General>Storage, when iCloud Photos is optimized, it shows 29GB. But when I "get info" from the actual Photos file on the computer, it shows that the file is about 330GB.
So, somewhere there is a discrepancy between 29GB and 330GB and what is being reported when iCloud Photos is optimized.
Does anyone have any ideas on how to address this? It also shows that the purgeable storage is like 400GB or something really high, particularly given the fact that it is only a 1TB drive.