I think some used them to gain insight in clicks (bit.ly provided stats for numbers, user agents etc.), and to track the origin of clicks by generating a unique shortened URL for each linking post.
Also, the obvious use case of turning a long direct URL to a file into something people can actually be bothered to manually copy from paper...
When it comes to email I just have my server reject any containing links that point to URL shorteners. I’m not stupid enough to click them anyway but it’s safe to assume you’re just a scammer or some other lowlife, even if you’re otherwise considered a reputable business.