The community is forced to deal with everyone's issues, rather then ignore the minority. It takes a long time. Consensus, working things out until everyone agrees what the best course of action is, can take a lot longer then just voting and going with the most powerful faction. People get tired of dealing with things, especially when most issues are discussed at meals where some people would rather be socializing. It's important not to be hurried, to be willing to discuss things through for as long as it takes, or even put a divisive issue aside for a while and come back to it.
Consensus is conservative.
Once you've decided something, it holds until everyone can agree on how to change it. But if everyone agrees the status quo is unacceptable, then it must be possible, if difficult, to find a change that everyone will agree is better. The minority can be silenced. Because everyone needs to agree on a decision, and because people sometimes don't want to spend the time necessary to arrive at a true consensus decision, there can be pressure against voicing dissent to the majority opinion, because it is seen as causing problems. Sometimes powerful personalities can dominate the process.