RAISERROR’s severity levels are defined in the Sql Server Books On Line, and give vague guidance about which severity level is best. The short and sweet is as follows:
- below 11 are warnings, not errors
- 11-16 are available for use
- above 16 are system errors
- there is no behavioral difference among 11-16
The best thing to do is just get everyone to use the same value and reduce confusion. It may be useful to use different values, to signal a desired behavior to the code that catches the error. In this case, a company standard or policy is in order. Also, keep in mind even though you may not use severities this way now, you very well might someday—in which case, you’ll be happy you started using them consistently now.