After years of thinking people were 'paranoid' for putting stickers/tape/etc. over their webcams, just yesterday I started doing the same thing.
Like most people, I also used to think the indicator light would always come on when the webcam was active (as in, it would be part of a hardware circuit or something similar), but I now know this is not the case (at least on my own laptops).
One example of this is the Prey anti-theft agent[1]. If your laptop is stolen, you can remotely take pictures using the laptop's webcam (similar to what happened in the many 'stolen laptop' stories we've seen on HN where images of the thief are then posted online). When I test out this feature of Prey on my own laptop, it successfully takes the pictures for me but the webcam's indicator light is never turned on. It's worth trying this for yourself.
Anyway, (IMHO) you're better safe than sorry since a tiny sticker isn't a big deal.