How many character classes are necessary for context-sensitive spacing rules?

[macnmm]

The list of character classes includes 32 classes, similarly to those defined in the JIS X 4051 standard for Japanese. However, the existence of a class should mean there is a need for distinct unique spacing rules for that class compared to the others. Are there that many different spacing rules? What other purpose would one use these classes?

[r12a]

Many of the classes appear to correlate with Unicode line-breaking categories. I don't know if that's intentional.