Replacing grates

[RobinC]

Yesterday was cleanup day for me where I worked through each grill/smoker I have and got everything all cleaned up. Most have seen action throughout the winter so there weren't too many nasty surprises. Inspecting a couple of my older grates I can see a few are developing a few rust spots/areas. I've got spare greats anyway so not a pressing issue but was curious about what's the general consensus on when a grate has "had it" and should be replaced?