For some entities, calling Entity:Activate after this will scale the collision bounds and PhysObj as well; be wary as there's no optimization being done internally and highly complex collision models might crash the server.
This is the same system used in TF2 for the Mann Vs Machine robots.
The hull does not scale properly with this function.
Issue Tracker: #2193
This does not scale procedural bones and disables IK.
Issue Tracker: #3502
From the "Biggify" option of right clicking an npc
ent:SetModelScale( ent:GetModelScale() * 1.25, 1 )