I would say it's not essential, I didn't really understood what the whole point of it was other than unlocking your phone in another way. It seemed like more of a nifty thing than an actual need.
However, since I got a phone with one, I find it especially useful, not just faster phone unlocking but also fingerprint protecting some important apps and banking apps.
It adds another layer of security on your phone and I appreciate that. I wish the banking apps I use supported a double layer of security, asking me for the pin code and fingerprint before accessing it. However they just let me pick one or the other. Bummer!
Now I do think, though, that the fingerprint scanner is a pretty nice feature to have, even to the point that I'd call it essential if you're looking for a new phone.