By default, transparency is enabled for the taskbar and start menu in Windows 10. This severely decreases battery life. It can be identified by high CPU usage by mdm.exe or high GPU usage when idle.
In my opinion, transparency does not contribute to improving the user experience. When I am working, I want to focus on what I am doing and not on what my computer is doing in the background. So I would rather disable transparency than leaving it enabled.
When I was playing a movie in Windows Media Player, and I would open the start menu in front of it with transparency enabled, I noticed my movie started to stutter while it was playing in the background. And I have a fairly fast ThinkPad W540.
To disable transparency:
Press ‘Windows key + I’ to open the ‘Settings‘ app, or open the ‘Settings‘ app from the start menu.
Then go to ‘Personalization‘.
Go to ‘Colors‘.
Disable or uncheck ‘Make Start, taskbar, and action center transparent‘.
Open the start menu again and notice how smooth it now opens.
You might also see a battery life increase by disabling transparency.