Benefits of starting both safeties of one team?

I drafted Quentin Mikell of the Rams earlier this year and recently picked up Craig Dahl. Do you think there'd ever be any benefit of playing both of them at the same time during certain matchups, or should I be trying to trade off one?

Case in point- this week, the Rams play Chicago. I'm starting a LOT of my Rams defensive players in preparation for the slaughter (Long, Dunbar, and currently Dahl). I've got Mark Barron (@ Dal) and Madeau Williams (vs. Cin) currently starting at S. Morgen Burnett (@ Sea) and Mikell are on my bench. Burnett's usually a starter but I figure he won't be getting a lot of action vs a very run-based Seattle offense (definitely starting DJ Smith at LB though). I picked up Williams off of FA this week and started him in hopes that gets a pick and a few tackles off of Dalton and his WRs. However.... Chicago's offense is seems to be a big, fat IDP points cow. So should I pull one of my starting guys (Williams, probably) and put Mikell in along with Dahl? What about in future weeks, as well?

This is an 18-team dynasty keeper league. 1.7 points per tackle and defended pass, 2.6 for sack, 3 for an int, 6 for int returned for TD.

Thanks again for all the advice!

I personally don't think it's a big deal to own safeties on the same team as long as they are producing. I like the CHI matchup this week as well. However, I also like Williams against his old team. Although, I have Mikell ranked higher, if I were a risk averse person, I'd probably start Williams. If you are willing to put your eggs all in one basket, go with Mikell.