What is the point of using interceptors to attack UFOs?
I understand most of what's going on in XCOM: Enemy Unknown, but I don't quite get what Interceptors are for. I know that when I Scan for Satellite Activity, I can come across a UFO, and then scramble Interceptors to attack it. If the attack is successful, then the UFO will crash and I can send in my team to fight them on the ground.
However, what's the point of all this? Is it just a random event where I can acquire more resources to spend on stuff? Does it have absolutely no bearing on the main storyline? Does it decrease panic levels?
Also, can I only encounter these events in areas where I have a satellite? Should I invest in strong weapons for my Interceptors? When I started the game, I had a choice between North America or Europe as my base. I'm glad I chose Europe because Research seems far more useful than Interceptor upgrades, at least for the time being.
It is in fact an event where you will get a chance to get more resources. This is really important; you need to acquire certain materials to do certain research to get a path to victory in the game, and that says nothing of getting your soldiers properly outfitted.
As to the randomness, that's not likely. The aliens have an agenda and it will play out on the geoscape. UFOs have missions; shooting them down prevents them from carrying those missions out. Allowing the aliens to carry out those missions will help spread panic/alien presence (at a high level) which is bad for you.
I have only ever seen ufos where I had satellites deployed. Eventually you will need to upgrade interceptors as they will start encountering much larger, more powerful craft.