I've seen the "fat comma" used in a number of situations like this, where it can be said to indicate that its left operand "becomes" its right operand in some way.

Fans of this usage think that it makes their code clearer. I strongly suspect that, in most cases, the opposite is the case. In my opinion using the fat comma for anything other than hash initialisation can be very confusing. And in his new book Damian seems to agree with me as he strongly suggests only using it for defining key/value pairs.