Under Administration -> System -> System Behaviour, the Maximum number of occurrences value is used to define the maximum number of repeating appointments that may be set. A query may arise regarding how high that value can actually go.

More information:

Detailed performance testing has not been carried out against the maximum number of occurences that may be used; values higher than 200 are commonly used on customers' installations. The point of the maximum number of occurrences isn't so much that the numbers of occurrences themselves are limited, rather that there is a limit.
This is due  to the differing architecture used between Sage CRM and Exchange - whereas for Exchange the occurrences are attributes of a single appoinment record, in Sage CRM occurrences are stored as additional records on the Communications table. This is the reason why recurring appointments with no end date are not supported in Sage CRM.