No, it’s not essential but it is extremely helpful. If you wanted to play other styles like pop, jazz, blues etc, then you could maybe consider learning classical alongside the style of your choosing.
When you first learn to read music and play notes on the piano, my advice would be to focus on learning the basic theory before worrying about style. Once you can sight read fairly well and you are comfortable with finding the notes on the piano pretty quickly, you can then consider which style you would like to branch out to.
The problem however with ignoring classical music altogether is that you may run the risk of under developing your hands, and the reason why I say this is that classical music will push you to the limits and teach you how to play everything you’ll ever need. If you are completely against playing classical music at all, then it’s still possible to ignore it altogether and move straight onto something else. There are many famous jazz pianists for example that didn’t learn to play classical or read music very well, and they didn’t do badly for themselves! But for most of us, learning to play the piano means we have to train our hands, and make them quicker and stronger. Scales are also the best way of doing this, mixed with playing classical.
It does also depend on how far you want to go, because classical music can get very serious and time consuming when trying to learn. So if you are only looking to learn a few tunes then by all means don’t put yourself off by dragging yourself through pages and pages of Chopin. If you have a favourite pop song that you want to learn, then feel free to jump straight in. You just have to be prepared for limitations that you put on yourself, and be open to the knowledge that you may not be able to play much more.
Most people I speak with who have been playing for years without classical training regret it, because they know they’ve limited themselves. It’s human nature to want to keep progressing onto harder pieces. So even if you do only want to initially learn a few straight forward songs, you will most likely have the hunger to keep pushing further once you’ve mastered something. There are only a few naturally gifted people that can continue without proper classical training, but for the most part your fingers just won’t be up to the speed and control that’s required for a difficult piece, no matter what the style.
My personal opinion on how to approach the piano is to learn and play classical to begin with, and then learn a style of your choosing alongside. That way you get the best of both worlds, and you will continue to progress and get better and better.
Finally, it’s worth mentioning that learning and playing popular music can be extremely worthwhile when it comes to understanding keys and chords – especially if you want to play in a band. Some pop song books for example will only give you the right hand melody and a chord letter. Which means you will have to figure out for yourself how to embellish and add to the song with your left hand. I’ve spent many years playing from pop books and I’m now able to naturally follow just the right hand with the chord and play a full left hand without music, and even add more notes with my right keeping the melody note to the top (little tip).