It matters because of code readability, debuggability and all sorts of code hygiene reasons. If I'm using size_t for a field in my protocol on a 32 bit platform

It matters because of code readability, debuggability and all sorts of code hygiene reasons. If I'm using size_t for a field in my protocol on a 32 bit platform on one end and 64 bit platform on the other, which size wins over the wire? Can that question be answered while in debugging flow trying to track down a memory stomping error?