Sony A900 metering question

I've tested metering while in M mode, shooting MLU with my eye away from the viewfinder, both with and without closing the eyepiece shutter. No difference in exposure / histogram.

I do see a shift in exposure w/ the eyepiece shutter open if I'm shooting in A or S mode (as one might expect from light entering and affecting the metered light).

My question is: is there any "other" reason to close the eyepiece shutter when working in M mode, since it does not impact metered exposure reading or anything I can see as degraded image quality in the files from light making it to the sensor?