Until now, lacking hard data, I was a believer that instant start is worse for T8 lamps than magnetic rapid start and shaved away more life each time the lamp is started. It's quite the opposite and by a significant margin based on a study.
Industry standard testing is 3hrs on and 20m off, but obviously to experimentally obtain data naturally, it would take way too long, so to study the effect of frequent switching, they used a 5m on/5m off cycle.
They tested seven different models of ballasts and each model of ballast was given a sample of 36 lamps. All the ballasts tested were 2 lamp type, so I think they had 18 units of each ballast model going at once, each driving two lamps.
The median cyclical lamp life of two magnetic rapid start ballasts were 2,800 and 3,100 cycles.
The median cyclical life of two instant start electronic ballasts were 13,500 & 19,500
Values were similar for two electronic rapid start, although one electronic rapid start hit 43,300.
This shows that in short cycling, which is often seen in residential use, lamps last five times as many switch cycles compared to rapid start magnetic.
So, I conclude that in frequently switched F32T8 applications, the lamp life from best to worst is:
A. Well designed electronic programmed rapid start
B. Electronic instant and rapid start
C. Magnetic rapid start
It's also well understood that magnetic gives the worst system efficacy.
You can see the report here:
http://www.lrc.rpi.edu/programs/NLPIP/pdf/VIEW/Guide3.pdf