URL shortener, plus image and file sharing.
I love ow.ly and Hootsuite. The analytics can't be beat by any other Twitter management dashboard.
I will say though, the feature "users who also tweeted this link" can be confusing and misleading to clients or novice users, as they think that a big brand or influencer re-tweeted then.
I use this for an account that I manage to host coupons on. I like the service, but wish it was integrated better with hootsuite and offered stats for how many times the files/images I upload were accessed. Whether the information is in hootsuite or ow.ly wouldn't matter.