I use Linux Mint MATE to watch movies with that I also use VNC. I have my PC set in the power options to deactivate or put the display into "sleep" mode after 10minutes. While I was watching a movie in fullscreen, 10min had gone by and my desktop began to fade (I thought it was the movie). So basically, the display settings for when it goes inactive should not apply to fullscreen apps or VLC Media Player etc.
Thanks, I love MATE, very lightweight and fast!