Do social proof apps really boost conversions?

In the left corner of this screen (on desktop) you'll see a notification every 15 seconds on a different action someone has taken.

"So and so just downloaded the Sidebar Plugin"
or
"Someone from woi woi just left a review on the Facebook Comments plugin"

They are called social proof apps.

Little pop-up notifications that tell you what other people are doing on your site.

The idea is you'll see someone taking an action you want to take, we're more inclined to feel comfortable doing it do.

But once you get past the novelty, does it really work?

Optimize, CommerceRas OMARI