L/600 Mechanical + DL deflection limit

[Chrud]

Recently I have been seeing more deflection criteria on structural drawings w/ open web steel joists that state joists must be designed with L/600 deflection limit for mechanical weight and dead load only. I'm not quite sure where this criteria is coming from.

 

[Deker]

Perhaps they are trying to reduce the chance of rain ponding on a flat roof?