The basic idea here is similar to Rote Learning:
Avoid expensive recomputation
Macro-operators can be used to group a whole series of actions into one.
For example: Making dinner can be described a lay the table, cook dinner, serve dinner. We could treat laying the table as on action even though it involves a sequence of actions.
The STRIPS problem-solving employed macro-operators in it's learning phase.
Consider a blocks world example in which ON(C,B) and ON(A,TABLE) are true.
STRIPS can achieve ON(A,B) in four steps:
UNSTACK(C,B), PUTDOWN(C), PICKUP(A), STACK(A,B)
STRIPS now builds a macro-operator MACROP with preconditions ON(C,B), ON(A,TABLE), postconditions ON(A,B), ON(C,TABLE) and the four steps as its body.
MACROP can now be used in future operation.
But it is not very general. The above can be easily generalised with variables used in place of the blocks.
However generalisation is not always that easy (See Rich and Knight).