Existing 3rd party software migration
Two notable differences between 'old' Rosetta and 'new' Rosetta are:

Rosetta 2 will 'pre-compile' its translation before the app is launched. The old Rosetta would 'translate' PPC code to Intel anew each time the app was executed.

PPC CPUs were 'Big-endian' (the order in which multi-byte words were stored), whereas Intel and ARM chips are both 'little-endian'. That removes one of the major headaches and causes of problems in translation.