Slurping is a simple mechanism by which the drinker aerates the tea, a practice also common to wine tasting. The main difference here is that whereas in wine tasting the liquor is simply sloshed about inside the mouth, in tea tasting the liquor is slurped. Admittedly, some people do find the noise associated with the tea version bit unpleasant, but there is a purpose to it so bear with me.
Because slurping cools down the tea, it can be served and drunk hotter and faster. To me, however, experiencing the tea as fully as possible is always the primary consideration, and slurping works towards that as well. When tea is slurped, the aromatic oils it contains are sprayed all over the inside of the mouth, and while this may not provide a more fragrant cup per se, it noticeably alters the character of the liquor by emphasizing some characteristics and playing down others, sometimes dramatically enough to make what seem to be entirely new tastes emerge (depending on how much you choose to slurp). As an added benefit, I have found that slurping often mitigates the appearance of excessive bitterness or roughness in the aftertaste of many teas; useful for rendering an overbrewed cup more palatable.
These differences may seem fairly minor, but then to slurp or not to slurp was not the existential question posed by Hamlet. The tea experience is rich in subtle nuances, so slurp to explore (and once the tea has been swallowed, exhale deeply through the nose for a few more)!