I generally follow the NMRA guides. With the .15 oz per inch and a meter showing only 0.1 increments, I may not get it exact.
I used to go just over, if there was a chance it would be light. Now, with a helix, I go a bit light.
When switching, especially pushing, I notice a difference with weighted cars. And, I do have problems with 89 ft auto racks on my helix, even after cutting the trip pins. The only ones that resist the lateral force enough to stay on track are the MT racks, which, with that acrylic insert, weigh a whopping 2.2 oz (NMRA would be about 1.5 oz. But, even weighing my RC racks to that, they still pull off the track when MT don't.
I haven't weighted them all to 2.2 oz, but have considered it, even if I need 3 Katos on the front and 2 pushers! Bascially, I don't run long cars down the loop now.