If you're watching any channels (even non BBC) you legally need a licence. It doesn't matter if they are Sky, Freeview, Virgin, digital, etc.
If you watch iplayer you now need a licence - it didn't used to be that way if it was only catch up.
You can watch Netflix, Amazon Prime, DVDs, use consoles attached to a TV to play games all without a TV licence. And radio programmes, including BBC radio stations and radio on iPlayer.
It's fine not to have one but you should be aware of what it is required for and what it isn't. I cancelled mine, and you can go and fill in a form online saying why you don't need one, they will stop harrassing you.