Buy one. Learn how to use it. Then sell it on if you decide you can live by trial/error/chimping.
If you "learn" to light by trial and error, should a problem arise and you do not fundamentally understand the mechanics of what you're doing, you're going to have to rely on trial and error to solve the problem, which may or may not work out depending on your time constraints.
If you know what you're doing and why, with a lightmeter you can set your lighting up without shooting a single frame. Even if you tweak your lights and use the lightmeter to check, it looks a damn sight more professional than chimping the (non calibrated, poor quality) LCD on the back of the camera, which is what every model has seen their uncle do at weddings.
I really do wish people would learn to understand what they're doing, instead of stumbling around expecting trial and error to win out. Dean Collins is spinning so fast in his grave it's a surprise GE haven't hooked him up to a generator.
In the context of your actual question: Not essential in the same way clothes are not "essential"

You can get by without, but in the long run it's better to use them.