It has to do with the notion that it is creating a new paradigm and idiomatic system inside of Perl that is actually much more constraining than what Perl already provides itself.
This is what you want when doing complex stuff. You can, of course, limit your data and application behavior with plain old Perl, but in the end it's too much work. Perl is not exactly at the top of elegant OO approach by itself. I've done some mildly complex stuff with Moose in the past and it worked great. I'll certainly use it in the future, although there are simpler alternatives these days.
and I am not sure what the payout is
The payout is simpler code, easier to understand at glance, easier to maintain and extend. For simple stuff, Moose is overkill, but for anything complex (in terms of behavior, not just in terms of pure amount of object data, methods etc) Moose is a good solution.
