Animals have a natural instinct to meet their mineral needs by seeking out different sources of nutrients to absorb the amount of minerals and vitamins their bodies require.
Lick blocks are very conducive to this natural instinct. The animals can use the licks at their own will (free will) and according to what they individually need.
The great advantage of a "free will" supply is that most deficiency symptoms and resulting diseases do not occur. The animals remain vital and healthy and are more resistant to diseases.