Does anyone see any drawbacks to adding this? I think I like the effect, but want to use it longer during everday use to see if I still like it or whether it become annoying.

Here's the theme I've enabled it in if anyone would like to try and provide feedback: (It only seems to work for the menus. Won't work for nautilus or rows/cells.)

-Transition causes the background to fade into the selected background color for a specified duration.