If you develop using a single language, a single framework, on a single machine, you definitely don't need Docker.
For every other scenario ... It's not perfect but I haven't seen anything getting anywhere close to the convenience it gives us.
It's really impossible to describe where docker fits into a development flow. The answer is always difficult and often quite hacky at best. After 6 or so years I'm still not convinced docker is for developers (if you can even define what a developer is).