... to ISRs. You can use it in the same way to preserve registers content in any subroutine or part of a routine in the "main" program; or you can use it if you need to use a lot of memory say in complex multiple-precision arithmetics, or more than two pointers for @Ri operations.

The point is, that instructions using registers tend to occupy less code memory and are faster (especially in the modern single- and four-clock derivatives) than those using direct or indirect memory access. However, it has its limitations due to limited number of registers, and the bank switching itself is slightly cumbersome.

JW