I don't stop but the gardening books say 4 trusses for outside and 7 for greenhouse. This is cordon varieties. Bush varieties they don't really say apart from keeping things tidy and preventing tomato fruits from lying on the ground where they get slugged and rot.
It sounds like a good idea, but not when blight is around because it causes a wound and every open wound makes the plant more susceptible to trouble. If you prune or top tomatoes, perhaps best at a time and in weather where wounds will heal over rapidly. Easier now that the weather is finally sunny.