Glass cover on hood

Guy at the local grow store told me that people tend to leave the glass cover under the hood off as to allow more light energy. This doesnt seem to make much sense, no? Plus how often do any of you remove the glass to clean the dust?

always leave the glass on . your room will be so much cooler. thats why you bougnt the nice hood. I only clean mine between grows. Dust off weekly.

Definitely. SOunded ridiculous to me. Thanks man