I like to borrow from the Music as Language analogy of Victor Wooten:
I am a pretty miserable speaker, reader and writer of German these days. "Ich kann nur ein bischen Deutsch gesprechen und gelesen." Sorry, Germans out there!
If I don't have some rudimentary vocabulary I won't understand what I am listening to. Because I have my limited knowledge of German I was able to get more and more acclimated to German by immersing myself in German TV, magazines and newspapers while I was on tour there. After several weeks I got pretty fluent (for me) but I always had my English-German dictionary and phrasebook.
As a listener who didn't play bass I knew the sounds off of records, I could even put my fingers down and imitate them on an instrument. As someone who learned the Music Language, I could say to myself, "Oh that's a Blues Progression. He is playing an 8th note groove. It's a lot of Dominant 7th Chords." and find things pretty readily. Like German, the more information I had the more I could understand what I was listening to.
An African Grey Parrot has a pretty wide vocabulary (maybe even mechanical sounds, a phone, etc.) but I'm not sure they know what they're saying.
If you like a certain style or wish to learn more about a certain style, understanding the Music Language allows you to more effectively analyze what it is you want to play. IME, the more you "think" while you are playing you are screwed-it's like thinking about every minute thing you do while riding a bicycle. You will fall over in 10 seconds if you think about everything you do. The more you practice anything the more second nature it becomes. The goal as I see it is to increase your vocabulary so that you're always in the Comfort Zone. My goal is to be "in the moment" at all times, even when sight reading. It can be done, but it takes time, lots of hard work in the practice room and understanding.
If an aspiring player knows a very limited set of information, he will only be able to process so much at a time. The first time I attempted to play a Jazz Tune (I think it was Autumn Leaves) in a Jam Session, I failed miserably because I didn't understand the progression. I was frantically trying to listen to what was going on around me, but there was so much information coming at me my 17 year old brain couldn't process it. As I practiced, studied and began to understand how this all worked (chord progressions, ii-V cadences, walking lines, etc.) it became no big deal and now 40 years later I can pretty much nail the changes of a tune after one pass if I don't know it and "fake" the first pass pretty successfully. That's because of a lot of studying so that the vocabulary is second nature. I think that's Jeff's point.