[Bahamut]

It gets necessary at some point - it's not cheap finding highly skilled full stack developers, and they're not the most common beasts around. Everyone wants them, but they have their pick of jobs. It's far easier to hire for the positions separately, and if your company is in need of rapid expansion, I'd say almost necessary given the market.

While I term myself as more of a frontend developer currently, I also know CSS pretty well (I sometimes fix bugs the UI team can't figure out), and I am currently transitioning to doing some backend work at my current job as well.

All developers should strive to be full stack, and designers should strive to know code more, but realistically speaking, not everyone is there yet of course, so you have to focus on developing the talent or hiring it.