Sometimes it is not possible to choose a "beautiful" solution for Your buffering. Usually it is as You said the time that is playing against us. It can also be other factors like code size, not having RAM or just that the sapplication does not need to be that sophisticated.

But it You have the luxury to be able to choose then the architecture that gives the most understandable result is propably also the best.

In the 80's I was coding a mobile terminal that had this FSK modem and a very complex protocol involving bit interlacing and ECC (Error Correction Code). At that time the microcontrollers were far from easy to program and available resources were scarce. I still have the ElanE12B Programmer in the attic.

The project was dealing with Maritime Safety so everything You did had to be thoroughly documented, reviewed and tested. In a task like that You really want to avoid any fancy solutions and You want to make everything as simple and understandable as You can. For those who are interested, the project (back then) was the DSC for GMDSS

Flexibility also means that You are able to reuse the code more often. It is not only the matter of not rewriting the code, You also skip module testing and the documentation. This is a real relief if there are extra demand on code reliability. I remember this project where the device was delivered into a place (orbit) where it no more was possible to make any program changes to the core functionality.