That works for the problem with user accounts and passwords, but there are other things that are left hanging.

I do not know exactly what is the reason, but these things affect especially unit startup when Harmattan is ran as 2nd level boot under ubiboot.
If the device is not correctly prepared, there's going to be a lot of process trashing in startup, and some devices / variants are more susceptible to this. In worst case it means that device will not boot, or will do so slowly or not every time.

If this procedure is done like I described, then this will not happen, the device will boot cleanly.