Sparring is probably my favorite aspect of martial arts training. It's the closest to a real fight that you can experience safely. That being said, doing it too much can lead to a false sense of security. Here are some of the key differences between sparring and fighting:
In sparring, your opponent's goal is to get bragging rights at your school or win a shiny medal/trophy. In a real fight, your opponent's goal is to put you in the hospital or the morgue.
In sparring, there are rules to ensure the safety of you and your opponent. Additionally, unless you are doing MMA, certain aspects of fighting (i.e. grappling if you are doing karate) will probably be banned. In a real fight, there aren't any rules. There is nothing to keep your opponent from hurling you through a plate-glass window if you miss that jump spinning back kick.
In sparring, it's one-on-one and your opponent isn't armed. In a real fight, your opponent will probably have friends who would consider a lopsided beatdown a male bonding experience. Additionally, he may relish the opportunity to try out his new baseball bat, switchblade, or .45 caliber (bang!).
In sparring, it's usually light contact if there is a significant size/age difference between you and your opponent or if it's a mixed gender contest. In a real fight, that 300-pound musclehead is throwing that haymaker at your 150-pound body at full force. That teenager might see little kids and elderly people as soccer balls with arms and legs. If you are a young woman, that not-so-romantic date who is pinning your wrists above your head does not know the meaning of "no", much less "light contact."
In other words, sparring is a good overall test of your technique and tenacity, but it won't completely prepare you for a real fight. For those life-threatening situations, you will need to do combatives drills, especially ones that deal with multiple opponents and armed assailants. Will they get boring after a while? Yes. Doing the same thing over and over again always gets dull. But repetition will grind them into your muscle memory so that, if you are attacked, you can defend yourself on instinct. That way, you won't be totally screwed if you find out that you brought your fists to a gun fight.