Sure, pc emulation on a classic Amiga, or even "NG" options isn't an alternative to having a physical PC if one wishes to use an even moderately recent version of Windows, but there's a universe of cool, useful older software out there for dos and win9x.
Despite having a dedicated Win9x box (I like seeing how useful older systems can be in the modern world) I actually use Dosbox + RunInDosbox for some productivity software on my AROS box. According to Sandra SiSoft plus a few other tests I get roughly 550mhz interger and 750mhz fpu p3 type speeds, which is more than enough for things like Paintshop Pro, 3d Studio Max, console ROM hacking tools, Unreal, Unreal Tournament, etc, etc.
The ppc options are more along the lines of a mid to higher spec 486, but even that's enough for some productivity stuff and early 90's games.
Even slower again, but 68k machines are also capable enough to run some software that doesn't exist on the Amiga.
It all depends on what sort of software a person wants to run, but in my opinion PC emulation can be useful on Amiga-oid systems.