I can tell you from recent experience that it does cause terrible lag over the whole region it is used in. If you were to use it on a 200 prim house you wouldn't be able to do much of anything. I had a renter using between 32 & 74 Temp-On-Rez prims and it shut down my neighbours dance club due to lag and music stream malfunction. We have had to add a proviso in our rental policy banning their use in our skyboxes.