In general, a window in any wall or door make is less insulated than its surrounding door material. Not knowing you door material I can't say for sure, but I assume you would be letting heat in the summer/cold in the winter to some extent.

I would also check if the glass in the garage door is double pane, gas insulated, etc. as that can offset thermal properties. If you're really concerned about windows letting in cold, I'd recommend a non-windowed door.