Here is the scenario:
I find a source for a profile that I manage. I edit my managed profile, create bio, add source. I probably do the same for the person's spouse.
Now I have a choice. I can move on to my next profile, or I can add the source to the children, children's spouses, grand children, children's spouses parents, etc. and whom ever else are also mentioned. Assuming I do that for a few (dozen) pre existing profiles, now there is a source on the (usually unsourced, gedcom imported profile), but no bio. In a perfect world I would have unlimited time to create a bio for every person mentioned in the source regardless of how peripherally related they may be. But I don't, and until wikitree decides to pay me per bio, I probably won't. I do what I can, but I can't do it all.
Again, I can just move on and assume that the profile manager will be notified that the profile has been updated, go see the change, follow the link I've provide to the source and create a bio for the profile. I would love to think that is the case, but probably not.
This is the point I would like to add the profile to a maintenance category so that those that have a few minutes to spend can pick up the now sourced profile and create a biography from it. I hear some folks like to do the narratives more than the research. I happen to like the research more than the narratives. I am thrilled to have a place where we can all contribute to our strengths.
The categories already exist, or the framework does. Templates just make it that much easier, especially for the more casual users.
Rule to live by: Make it easy to do the right thing.