Some Other benefits

Smaller systems contain fewer bugs, of course, but they also tend to have a much lower defect rate. A recent study by Chu, Yang, Chelf, and Hallem evaluated Linux version 2.4.9 In this released and presumably debugged code, an automatic static code checker identified many hundreds of mistakes. Error rates for big functions were two to six times higher than for smaller routines. Partition to accelerate the schedule, and ship a higher quality product.

NIST (the National Institute of Standards and Technology) found that poor testing accounts for some $22 billion in software failures each year.10 Testing is hard; as programs grow the number of execution paths explodes. Robert Glass estimates that for each 25% increase in program size, the program complexity—represented by paths created by function calls, decision statements and the like—doubles.11

Standard software-testing techniques simply don't work. Most studies find that conventional debugging and QA evaluations find only half the program bugs.

Partitioning the system into smaller chunks, distributed over multiple CPUs, with each having a single highly cohesive function, reduces the number of control paths and makes the system inherently more testable.

In no other industry can a company ship a poorly-tested product, often with known defects, without being sued. Eventually the lawyers will pick up the scent of fresh meat in the firmware world.

Partition to accelerate the schedule, ship a higher quality product and one that's been properly tested. Reduce the risk of litigation.

Adding processors increases system performance, not surprisingly simultaneously reducing development time. A rule of thumb states that a system loaded to 90% processor capability doubles development time (versus one loaded at 70% or less).12 At 95% processor loading, expect the project schedule to triple. When there's only a handful of bytes left over, adding even the most trivial new feature can take weeks as the developers rewrite massive sections of code to free up a bit of ROM. When CPU cycles are in short supply an analogous situation occurs.