I agree with a lot of the other answers but let me give you some backstory on what we did.
When I had a photo studio, we had 4 distinct websites. They offered something unique - each photographer's portfolio and the opportunity to book exactly who you want.
So we had:
- Studio
- Owners
- Associate 1
- Associate 2
So our main studio had our branding. It showcased everyone, was very "newsy" about the studio, etc.
Our owner site was an overlapping brand but you could only see the owners work, owners about page, owners everything. Even the contact came directly to me, not our sales@ address.
Associate 1 and Associate 2 had completely different branding. They were based on the personalities of our photographers, not our main business. If someone was more interested in a fashion photographer, they wouldn't want us, they'd want our associate1. If they wanted more of that rockstar grungyness, book associate2.
So the plan was simple - dominate the SERPs on our main keywords and then sell to those who wanted each brand. It worked beautifully. We were one of the most booked studios in my area (maybe shot the most weddings between 2009-2010.) Associate1 grew past our business and now has her own studio. It was a tremendously successful plan.
If you offer something unique per site or at least some reason to get backlinks to more than one "business" it can work. I've MADE it work. But if you're just going to double up to hedge bets, it won't work. You'd be better off ranking #1 for your main than #8 and #10 no matter which study you believe:
http://searchengineland.com/organic-click-thru-rates-tumbling-study-97338
Of course, position 1 + 3 beats 8 alone. So it just depends on the situation.