CLUSTER and clustered indices

When a table has been CLUSTERed on a particular index AND that index
values is monotonically increasing, then it would be a bad move to use
blocks from the FSM since this would tend to destroy the natural
clustering sequence.

The index values will be monotonically increasing if a datatype is
defined as SERIAL or if the default value is defined as the nextval of a
sequence.

Does anybody think it would be a good idea to not use the FSM if
- we have a CLUSTER defined on an index
- for the indexed column we have default value set of nextval()

Best Regards, Simon Riggs