I too have wondered this in the past, when doing my own tree - from my own experience this is my advice.
1. Don't just keep adding people with minimal bio and one source, intending to come back later to add the rest of the information you have - I did this at first and ended up with so many half done profiles I was so confused about which ones I had/hadn't fixed up
2. Don't try to add everything to every profile one by one - I tried this too, and found it really hard work, as I made so little progress each time I felt quite exhausted and discouraged. I thought I would never meet my expectations.
Conclusions:
* Mix it up, do a bit of each - you will feel more satisfied with your progress, without sacrificing quality too much
* Just add 5 - 10 profiles at a time with bare bones, then flesh each of these out with all the details and sources you have at hand, before adding any more new profiles
* Every now and then pick 1 or 2 existing profiles to improve to the best of your abilities (and access to sources) - review the profile, check for errors, and do some research to see if you can fill any gaps or add extra info. New sources often become available, and you will find you get better at writing bios with experience. You will feel very pleased with yourself when you see the result!
Best Wishes and good luck with your WikiTree experience
Christine