Should a MySQL slave used for backup also be used to service read-only requests in a production environment? Based on best practices, I'm wondering if we should have at least one slave that's used solely as a backup server, without servicing any forward-facing requests from users.

For example, if we have a master server with a single slave, and that slave is used to back up data via mysqldump a few times a day, are there any compelling reasons not to use that same slave to calculate some quick-to-load (&lt;10 seconds) analytics for a handful of customers in production?
Not a proper slave because you are not using mysql replication but anyway it's very common to have an slave or more than one to reduce the load in the master server.
Make really sure that its only used for read queries.