H.W. Brands says we'd be better off without them:
Candidates are rarely tested on the most critical quality required of a president: sound judgment on serious issues. The debate marathon that has marked the Republican season so far has been especially unhelpful. This reality show of campaigning bears as little resemblance to real life – in this case, the real life of responsible governing – as reality shows typically do. In fact the debates have probably diminished voters' chances of choosing an effective president. Debates reward candidates for one-line zingers rather than thoughtful responses, and they condition voters to expect slogans for solutions to complex problems. Intra-party slugfests like the Republican series drive discussions to the extremes, making more difficult the inter-party compromises that will be necessary to get the economy moving and the deficit under control.
I have to say that, regardless of their limitations, exposing these candidates to hours of questioning does help inform us about who they are in an as uncontrolled a setting as we can imagine. It was the only time when we got to see Sarah Palin without a protective filter. Perry's awful performances have also helped reveal the dumb-as-a-post, lazier-than-thou bullshit that can work for a crony-ridden Texas governor, but not on a national level. Yes, I know they can be excruciating at times. But they help show human beings in a few precious moments off-script. Their emotional temperament comes across. And that matters.