Historically they spammed committers of force-opted-in repositories with an email on every commit to tell them what their new BTC donation balance was after the commit. And they insist that once a repository has been added to their system, they do not have the ability to remove it.
This has legal and tax consequences they seem to be blissfully unaware of, and the best they'll offer is to stop sending you an email every time you make a commit.
We (meaning the Django project) went a few rounds with them a while back and ultimately had to resort to threatening spam complaints against their ISP just to get the damn emails turned off. We still have been unable to get removed from the list of projects they "helpfully" collect donations for:
https://github.com/tip4commit/tip4commit/issues/111
The link in this thread is another major developer also attempting to get his repositories removed from their "service", and being stonewalled just as we were.