You do not 'need' to complete your Artist profile. Incomplete profile will not prevent your Release to be delivered to the stores.
However, the more the better.
The 'Artists' section allows you to add some information like artist' bio, website, twitter channel, facebook page, myspace link...Etc.
You can also upload a picture with the following specifications:
- 3x2 aspect ratio
- Minimum size 1280 x 853 pixels, Maximum size: 2530 x 1706 pixels
- Format: jpg, tiff or png
- Max. 8Mb
Not all stores will take this information into account, but some will.
Adding a biography especially can help you get more exposure on stores and provide additional interesting information for your fans!