>>1672626imo having a rear brake is sensible if you have brake levers on your main riding position like with drop levers on a drop bar
pros:
>can ride faster with more confidence in tire grip like with trail braking in corners or riding on slippery surfaces>arguably better emergency braking (some sources claim you can stop the fastest with just the front brake at least in a straight line on a dry surface but some riders might prefer to use both brakes)>redundancy in case the front brake fails>more even rim and brake pad wear, especially in the winter with road grit you can switch between them or if you want to gradually slow down you don't need the max stopping power of the front brake so you can use the rear brake>less fatigue from "engine braking">having an unused brake lever triggers autismcons:
>cost (if you don't already have it)>adds a couple hundred grams of weight>marginally more maintenance>might get hate from reddit fashion police 