If you spend any decent amount of time raiding you know that fight mechanics tend to range in the 30s - 2m range, and that 3m CD's almost never line up with fights because the CD is so long. As well as all the other issues that go along with strong 3m CDs.
Boomkins were a perfect example of this where they had this massive burst for 30s out of every 3 minutes and then did pretty much nothing for the other 2 minutes 30 seconds.