Back in 2013 I had a website with CoinURL BTC-paying shorteners and A-Ads advertisements. CoinURL pretty much scammed me (they had a withdrawal limit, I withdrew once I hit that limit and they never sent the money neither did they reply to my e-mails), while A-Ads is still running over there but I'm only getting a few satoshis a day now because I haven't updated the website in years so it's pretty much dead.

One thing I noticed is that my website's shortened links got significantly less clicks than those non-shortened. It's most likely for the same reason BrewMaster said a reply above: you never know where you're going to be redirected and it could be a fake website or a phishing trap. I haven't used it for such reasons, but many surely did.

Therefore, my advice is:
  1. Make sure you do a background check of the services you're going to use for link shortening or for advertisements because you don't want to work in vain
  2. Remember that hiding your links means less traffic