Supersport racing for a factory rider is a double-edged sword, and a sharp one at that.
In the long list of positive ramifications a rider can bear witness to if he agrees to ride Supersport in addition to duties on a Superbike, is lots of cold hard cash.

Make no mistake: the 600 Supersport title, and likewise a Daytona 600 Supersport win, sells motorcycles. Manufacturers want to sell bikes (natch) and they put an amazing amount of resources towards Supersport, one of the first being hiring the best rider talent they can and paying that talent heavily because of his perceived talent, history or capabilities.

The Supersport portion of a rider's salary can be as much as 40% of the total. Win bonuses are within sight of the Superbike scale: $10,000 a win, $100,000 for the championship (at some teams). So, if you're a rider and you have the usual Superbike rider lifestyle where you buy $3000 lamps and $10,000 shifter karts, or expensive jewelry for your top-heavy girlfriend whenever she gets mad at you (which is often) without batting an eye, Supersport racing can make your life a lot nicer.

The downside is of course, risk. Risk is inherent in racing, and as was seen when Yasi Nagai died at Assen in 1995, anytime a rider steps off the bike at speed, there is a chance he won't be getting back on, even in the most innocent of slow crashes with plenty of run-off. Lost earning potential and death can occur in extreme cases, obviously. Keeping the amount of time a rider spends on the track to the absolute minimum to decrease risk is a cautious way of looking at racing. And not just because he can die doing this ...
In less extreme cases, a hypothetical rider falls off his Supersport bike and break some ribs and his Superbike title run is at risk (Mike Hale, Loudon 1995).

Let's say because of that Supersport crash, the hypothetical rider is not the AMA Superbike champion at season's end, his top-heavy girlfriend is spending time over at his rivals motorhome and he's trying to pawn his lamp, all the while wondering why his phone does not ring for days. For a rider, his value is determined by his performance in eight to twelve 72 hour periods (Fri-Sun race weekends) during the year. He needs to make things happen in that period in order for life as he knows it to continue.

For reasons like that, risk, riders like Doug Chandler swear off Supersport racing unless the factory really wants him to do it (and will pay well). Chandler does not feel the outcome is worth the risk in most cases. Colin Edwards II, on the advice of his sage father/manager, has never ridden a professional level Supersport bike in his life. Suzuki's Mat Mladin has never been crazy about riding a Supersport bike, as well, although he is one of the best at it.

Other negative aspects of riding Supersport are the amount of testing it takes to stay competitive, and the potential muddled thought process that can happen to the way a rider approaches Superbike when he has to ride Supersport. They can get bogged down in the variables.

However, the one factor few riders talk about in the plus column regarding Supersport racing is the amount of additional track time it gives them.

One thing you'll notice occasionally is the rider who spends the most amount of time on the track--being first out for practice and last in from qualifying--is usually the fastest guy, or among the fastest. Because every lap out there he is learning, and knowledge is of course power. Aaron Yates was third fastest in 600 practice this morning and second fastest in Superbike practice an hour later. Coincidence? Hardly.

Riding a Supersport bike doubles the amount of time a factory rider gets on the track. The racetrack surface is a constantly changing, constantly evolving mass of tar. Getting time on a Supersport bike increases the rider's knowledge of the track surface and traction, etc., keeps him in the zone, lets him keep an eye on his rivals, and in some cases the team can learn things on the Supersport bike that translates to the Superbike. That's why Nicky Hayden was both happy, and slightly unhappy with the decision made yesterday to stop his Supersport program.

Factory riders don't usually talk about it, but there are positive sides to having to ride a "streetbike".