Regardless of whether you sell online or in a physical store you need a target market. If you do not have a target market you will not use your marketing budget efficiently. You will just be trying to advertise to random people who may or may not ever want to buy your product. You need to identify who your market is so that you can market properly to them. That way you will not waste your marketing money and you will be able to more effectively craft your product so that it will appeal to your target market.
Yes, I also feel that whether you sell online or in a physical store you need a target market. So one should have to select a market enough that he/she can make that market notice his/her marketing efforts and he/she will get lots of potential customers from this targeted market. It is also good for business owners if they target small and specific market then their marketing expenses will be much lower and ideally it will good for them because they can invest their time and money in other activities also.