Sometimes you just don’t want to deal with the clients and the projects directly and you prefer to sell your stuff on some of the online marketplace. The most common are Envato, Creative Market and Etsy in case you are working with a physical products.
When you sell on these website pro thing is you don’t have to invest money on marketing and building your store. Your products gets sold by the platform that generates the traffic for you. Con is that their fees can be 50%, which means they are taking the big chunk of your earnings.
You can always open your online store but then you’d need the money to invest in marketing and somebody to actually executes the strategy.