So what are the advantages and disadvantages of "Map port using UPnP" for bitcoin core?
It lets Bitcoin Core ask the router to open the 8333 protocol port by itself, without you having to do it manually (a complex and error-pronne process that differs per router).
Disadvantages? There are not any that I know, because this feature extends only from the program (and computer running it) to its router. It doesn' incur any additional bandwidth costs.