Yup ... that's what I do as well. It makes the 'feeling' of the grip different, and thus ensures that I don't take my full swing grip because that would feel strange.

It's purely mental.

I also take of my sunglasses when putting. Not while reading the greens, but while actually performing the stroke. I found that slight distortion in the lense made it feel like I wasn't lining up right once I was over the ball. My vision out of the corner of my eye being slightly distorted.