Debates happen in just about any case you can think of but a few I think of are...
At School- In this case this serves usually for students to try to get an extension or try to help themselves if they are in a bad situation or miss something.
Debate Tournaments- This is more formal debating where they have judges and what you say matters and you need to make your point to win just like in any other situation that people debate in.
Running for office- For all kinds of elections from school council to running for president there are debates about contraversial issues in their communities/ countries.
At home- Often kids will debate their parents for things they want to do but their parents refuse to allow them to do.
In each one of these situation debating usually can help to resolve the problem and helps the other side to recognize where you are coming from. Like I said before debate tournaments and running for often are usually the only kinds of structured debate. For the most part debate is unstructured but still has the key parts of debate which is an argument between two sides with legitiment information to back it up. The decision making process usually is changed because most people after debating decide that maybe the other side isn't so bad. But also sometimes a debate will not effect the decision making process.