Message 1

Severity:	Serious (value = 2)
Default Action:	Warn (value = 1)
Description:	Running in Diagnostic Mode! Execution may be slow and/or excessive disk space may be consumed.
Detail:

Message 1 occurs whenever a Diagnostic object is attached to the executing Model via the Diagnostic membership and one or more of the non-default settings for that object might impact on the performance of the simulation.

In general you should avoid running with unneeded diagnostic switches enabled and only use these switches when absolutely necessary. Other switches such as those that toggle on/off certain log messages do not prompt this warning.