Braking.
Using or not using the rear brake has many variables, how much riding experience do you have, what type of riding do you do, and surface and road conditions.
Using both brakes will get you the shoertest stopping distance in a straight line. Of course as you all note the Vmax rear brakes can be locked up very easy as it is. Is an upgrade necessary? Well if it gets you a better feel for the rear, Yes. I tend to lock the rear brake (In a straight line and sometimes do not even know it)
This questions is like using two of four fingers on the front brake. Why do we teach four fingers in one class and two in another? Well we teach four fingers in the basic classes becouse we want the students to seperate braking from throttle. (Doing both at once can be bad with out proper technique. Now using two allows for throttle to brake trasition which helps the suspension, cornering and smoothness thru curves.
On the track, the coaches tell you to leave the rear brake alone, why, well becouse for new riders to a track as some of you know it will get you into trouble using it too much or at the wrong time. If it was not necessary or a good thing racers would just take them off to lighten the bike. Less weight is better!
Rear brakes are necessary and can help to make a smooth trottle to brake transition withgout upsetting the suspension! Do I need to upgrade my rear.
brakes? No , But some better front ones would be nice!
So upgrade if it gives you better feel or you want the bling. Otherwise you are money, time and experience ahead to leave it alone and work on your technique, Take a class etc.
I find it funny that some people will spend thousands to upgrade a bike to make it preform better or handle better when they will not pay a few hundred to learn to ride better. Case in point, I went to Louden for a track day with a 1992 Kawasaki EX500 completly street stock with cheap tires. I was the smallest bike, My first track day and first sport type bike. (If it can be called that) I lapped the field, and had a blast. Was riding around 600's, 1000's etc. It was a good time and I got to see first hand the difference that riding skill makes over bike preformance! (It is the Black and Red bike in the picture) I was wearing my Gray Stich on Wednesday and rented blue and white leathers on Friday for the second day)
So on Back brakes? LEARN to use them properly and use them well! Upgrade if you get a better feel or want bling, Like many things people do, they do it becouse others do, and many may not even know why.