I use it on a daily basis to discover the reasoning for things that happened before my time. I've never known anyone else who does this, and I've never understood why.
It's a weird way to try to save money, imo. Down the line it just leads to confusion and repeat work.
They also underinvest in documentation, with the same result.
YMMV, of course. But my mileage was pretty terrible.
My current job has both Basecamp and Slack. Most of the work discussion happens in Basecamp, which is fine. However, the search is pretty awful, so it's hard to get a quick and relevant response back when trying to find out more info about a given setting, feature, piece of code, or whatever else. There's a lot of extra digging involved with Basecamp's search results.