e.g. the slave micro can handle checksumming, retransmit (if required) and such. Also, it may, by buffering, be able to make the master transmit and receive "when convenient" rather than "when needed"

>>> the types with FIFOs make life so much
>>> simpler than those without
>> It's there in slightly different form, please check
> OK, I missed it.

No, but you can make the negative stronger and the positive weaker. Had I read this 25? years ago when I was a beginner with the '51, my conclusion would have been "no sweat, I can do that". Today, no more a beginner, my conclusion is "lots of sweat, let me avoid that, when the next upgrade happen timing problems will most likely pop up".