ThisDepends on your goals
ATP Flight School does it all the time. That said, you're not "knocking out two ratings at the same time". There's not much overlap between the two. Main benefit is you'll have more multi time, which used to be a golden ticket to the airlines, but not so necessary anymore.
Places like ATP will get you a quick private multi rating then have you do your entire instrument rating and commercial time building in a multi. It will give you a lot more multi PIC time than you would get otherwise, but it comes at a cost.