By dividing embedded software into a team of cooperating, memory-protected processes (containing threads), we can readily treat these processes as “components” to be used again in new projects. Because of the explicitly defined (and hardware-enforced) interfaces, these processes can be integrated into applications with confidence that they won't disrupt the system's overall reliability. In addition, because the exact binary image (not just the source code) of the process is being reused, we can better control changes and instabilities that might have resulted from recompilation of source code, relinking, new versions of development tools, header files, library routines, etc.
Since the binary image of the process is reused (with its behavior perhaps modified by command-line options), the confidence we have in that binary module from acquired experience in the field more easily carries over to new applications than if the binary image of the process were changed.
As much as we strive to produce error-free code for the systems we deploy, the reality of software-intensive embedded systems is that programming errors will end up in released products. Rather than pretend these bugs don't exist (until the customer calls to report them), we should adopt a “mission-critical” mindset. Systems should be designed to be tolerant of, and able to recover from, software faults. Using the memory protection delivered by integrated MMUs in the embedded systems we build is a good step in that direction.