Performing more than one chakra opening meditation at a time is not typically recommended; not because it's dangerous or anything. More because of the fact that your soul is gonna need more focus applied on each chakra to properly activate them for the first time.
Anyone is more than welcome to try to activate more at the same time but its just important to have this in mind: activating the chakras for the first time is one thing, but fully opening the chakras 100% is another.
And to answer your question on the good or bad, depending if your particularly sensitive to energy, the good that can come out of it is simply, "nice, I can activate/open more than one chakra at a time."
The only bad thing I can imagine happening besides wasting your time is you might gain more energy than your soul can handle, and it'll basically make you nervous, fidgety, a little more high-strung and altogether more sensitive. And that's really it, like I mentioned earlier, not dangerous or anything but you're more than likely just going to waste time.
And remember, to fully open them can take weeks, months, or years, so don't get too hung up on trying to open them as fast as you can. Just work on them every day with any of the meditations that help their energy flow better. And that can be with:
-Spinning them.
-Vibrating words of power into them.
-Breathing into them.
-Hatha or Kundalini Yoga
-The Serpent Meditations
And more meditations that I'm sure you'll get into with time.