Debating not only clarifies issues. It allows us to analyze our thinking. We can learn and see where we might be wrong. The goal is to eventually think things out thoroughly till we form an opinion or conclusion. Then we would debate this with other people and make adjustments to our opinions, that is if we are open minded.
Without it we wouldn't know the facts or get the chance to question our own thoughts. Some debates are conducted very professionally and clearly. I do believe though that instead of shouting opinions at each other, which seems to be the case most of the time, we can figure out a more civilized method. Especially in political debates, debaters know that even if they are wrong they can just keep on saying things their supporters want to hear and wait for the next topic. It is called the "Worser Argument." Why not list all the points of each party and have a group of people investigate them to see which ones hold true and which ones can be thrown out, then discuss the ones that aren't so black and white. This wouldn't be necessary in a debate amongst friends, but it would sure solve a lot of ridiculousness in politics.
And influential, if performed properly. Different points and opinions are presented, critically thought about, refuted etc. You may have never even considered a point or situation until presented in a debate. In politics, it is good to hear political parties debate issues in order to make an informed voting decision. Of course, some people can debate poorly, though that in itself is subjective, but all in all the mere act of debating is better (than not) in my opinion.
When you people debate, you usually debate semantics, not points. It is more a semantics-based argument than a logical, point-making debate.
There are those that are capable of debating. But please have the decency to not stoop to the level of semantics; it is below most of you users yet it is so common a mechanism of debating.