Mapillary is/was a private for profit company that allows people to extract information from their crowd sourced photos and then add it to OpenStreetMap. So a road sign or business name or whatever.
This arrangement encouraged lots of OSM users to contribute photos to Mapillary, as it is a nice way to add information to OSM (and to enable others to add information).
The indirect impact on OSM services is that turning on the view of the Mapillary images in an OSM editor will request that data from Mapillary servers (which are now Facebook servers). So you can go to the OpenStreetMap website and engage in an activity where you request data from Facebook servers. But you have to sign in, activate the editor and then activate the view of the images for that to happen.
A lot of the people that contributed heavily to Mapillary are disappointed with this outcome, as they have strong feelings about Facebook. I've contributed a little bit to Mapillary and will likely continue to do so, as I'm not trying to create an open data street view commons, I'm using it as a convenience.