The point I was trying to make is that you have to do a judgement call on LOAD.
When you drop the clutch and spin the wheels, there is significantly less load on the flywheel>clutch>gearbox>drveshaft>diff>half shafts...... then there would be if you did the same thing, but the wheels GRIPPED.
When you chirp gears, thats different to flat shifting. You're typically not transferring 100% torque through the driveline. (50% throttle or so)
heck, even some high HP cars will always chirp no matter how soft you shift =D
and of course, all of these techniques transfer more load then smoothe shifting.
judgement call at the time, get a better understanding of what your actually doing with these shifts, and you wont need to rely on forum opinions to tell you if what you are doing is safe.
Personally, at the 1/4mile, when your going for a good time, you want to chirp as many gears as you can, without spinning the wheels. But just know you are stressing the driveline. But you cant get a good time without doing so. it is a test of your car's capabilities after all...