The default configuration for SQL Server should be used unless you have a demonstrated problem that requires a different configuration. This is to include the Max Degrees of Parallelism for OLTP's as a well. Even for transactional work loads, parallel processing is beneficial if the hardware supports it. If you find large CXPACKET wait types during query processing, then you might look at changing the Parallelism setting to adjust, or setting it to MAXDOP 1 using query hints for problemattic queries, but you shouldn't change the setting as a blanket rule.