There's no need to remove internal rust if you're going to treat the insides with some lotion or potion. What the lotions and potions do is create an oxygen barrier, which will stop any further rust.

Having said that, I'm in the camp that this is a solution looking for a problem. It is extremely rare to find a frame rusted so badly that it's damaged. One exception that you sometimes see are around brake cable guides, where sweat accumulates and through capillary action gets sucked into small gaps.