What are practical differences between `REPLACE` and `INSERT … ON DUPLICATE KEY UPDATE` in MySQL?

Question

What I need is to set the values of all the fields of a record with a particular key (the key is composite actually), inserting the record if there is no record with such a

Answer 1

In what particular cases can REPLACE be preferred over INSERT ... ON DUPLICATE KEY UPDATE and vice versa?

I've just found out the hard way that in the case of tables with a FEDERATED storage engine INSERT...ON DUPLICATE KEY UPDATE statements are accepted, but fail (with an Error 1022: Can't write; duplicate key in table...) if a duplicate-key violation occurs - see corresponding bullet point on this page of the MySQL Reference Manual.

Fortunately, I was able to use REPLACE instead of INSERT...ON DUPLICATE KEY UPDATE within my after insert trigger to achieve the desired outcome of replicating changes to a FEDERATED table.