| As far as the quick-release sprocket carrier thing is concerned, I think it's not just about track-days, and changing sprockets frequently. Changing the sprocket on the stock set-up is a bit of a job: you have to undo the big nut and remove the whole rear sprocket coupling, then disassemble that.
Changing the sprocket with the quick-release set-up is a ten minute job.
So, depending on your level of mechanical competence/confidence, if that's the difference between paying a professional to do it for you, or doing it yourself, then it'll soon repay its cost. | 
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