Imagine you're in the office and people are raving about a series that's currently on Sky. You don't have Sky because you think they don't deserve your money - there's bad blood there and you've sworn off them for life.
Rather than eat humble pie and sign up with Sky you want to know where you can stream it legally.
You could browse Netflix and Amazon Prime etc or you could get someone else to do the hard work for you.
The first service you could use is http://wheretowatch.com which will search legal streaming sources to advise you on availability.
If it's not available on your platform of choice then you could use http://www.canistream.it. This site also searches for you but will also notify you when the show you are interested in becomes available on a particular platform.