When I open or edit a photo or video in Apple Photos on an 'optimised' Mac, does the full size file remain on my Mac forever?

Although I have plenty of space on my Macbook Air M3, I have a question about how Optimising photos and video in the Apple Photos app works.

When I double click on a photo or video in Apple Photos, a little white circle appears momentarily as the full file is brought down from iCloud. This allows me to see and/or edit the full-res photo or play the video.

My question is this… once downloaded to my Mac to see the full size file, does that full size file remain on my Mac forever or does optimising secretly re-'optimise' the video or photo again at its own pace?

Put another way, say I have a genuine 40GB of photos and videos in the cloud but the optimised file in 'Settings-Storage' says, say, 10GB and I open every one of them on my Mac, I assume the space used on my Mac will increase accordingly to possibly 40GB of used space. Now my Photos library is theoretically full of hi-res versions. Will Photos eventually re-optimise all these opened files to return the library to its former optimised size of 10GB?

Apologies for the convoluted way I'm written this. Your expert assistance much appreciated.