When you configure Bob's mods to have e.g. diamonds in coal then instead of getting a diamond once in a blue moon you always get one coal and one diamond. This means that you end up with tons and tons of diamonds right from the start, when you don't even have filter inserters, and no place to put them.
Kind of makes the game unplayable. Even with filtering every now and then the chest for diamonds is full and you get no more coal.