What is the reasoning behind the "urban" slang word "tight" coming to mean "cool/great/slick"?

Solution 1:

From thefreedictionary.com:

15 Marked by full control over elements or subordinates; firm: tight management; a tight orchestral performance.

In music it usually means all members of an ensemble are playing together with rhythmic and harmonic precision. I think it's not much of a stretch to work from that meaning to the sense of something being remarkable or "slick".

Solution 2:

Based on cultural proximity, I'm relatively certain that the usage in question came from music. However, I'm going to go ahead and suggest that some implied sexuality has brought the term down the ranks.