That's pretty much it, my customers are people who have websites and want to be the first to know when there's an issue on it so they can fix it, in which case a SaaS solution is usually better than some internal tools because it eliminates setup/maintenance, keeps working when all your infrastructure is down and monitors everything (including internet link). Some other clients monitor website they do not own when they depend on it, for example as a vendor I could monitor Amazon if I sell products on it to be aware of any issue, or if I'm a digital customer engagement platform (what my full-time job does) I can monitor services I interact with like facebook API, twitter API, etc.