As @scallioXTX said, it is important whether you want to make money or not... I would add to that... by selling.
If you're selling products or services, it is very important. Because that's what it means: traditional commerce moved to the online world.
And even depending on the product, it might not be that important. I mean, you don't buy a Ferrari online, do you?
So even if you have something to sell, e-commerce might not be very important to you.