I think a lot of people don't have torque wrenches or the tools to make this job as "easy" as an E50 still.
The fact is, if you want a long-lasting high mileage ZA50 then you do need to check the shimming when you open the transmission. But everyone should be encouraged to get the tools and do the work because it's totally worth it and not as hard as it might sound.
You should check the clearance between the top of the roller retainer thrust plate (funny looking washer that covers the rollers on the main shaft) and the the shim that goes on top of it, as well as the clearance between the clutch cover bearings and the respective shims on the crank arm and main shaft as mentioned already in this thread.
It's also essential to torque the clutch nut and the left hand thread nut on the main shaft to spec.
Most of the time, an improperly shimmed ZA50 won't result in a bike that won't run at all, but rather a bike that seems to run fine but will eventually result in the output shaft bearing in the transmission cover grinding itself free while you're riding down the road.
It's super easy to check the clearances listed above with the right tools (feeler gauges, plasitgauge) and a basic torque wrench, and it's worth it for the peace of mind. (edited)
