Mains, whether sofits or something like a Genelec 1036a, when done right, are very flat. They also are extremely precise. The problem is that very few people (none) have speakers that precise at home. It takes a lot of practice to mix on mains and have it translate. At least, this is the theory. I tend to think they sound too impressive for mixing. If I listen on mains, I can hear all the details that are lost on other speakers, so I don't try to keep things as clean.
Inversely, I really like mains for tracking, because I can hear all the details quite easily, which helps me know if something is going to pop up later which I need to worry about.
By the way, midfields and mains are very different things. Mains are far fields, and are hopefully sofit mounted (something which I do not want out of near- or mid-field monitors).
And then we get to the most important use for mains. They are what you pump the mix through when you do not want the client to question your mix. They will almost always love it through the mains. Client Impressers, as we say.
I wish I had some these days.
Light
"Cowards can never be moral."
M.K. Gandhi