Cattle will always voluntarily consume salt - usually more than what they need but not enough to cause a problem or cost very much.
Cows will crave calcium and phosphorus if they are deficient at a metabolic level.  That is - they will crave enough calcium and phosphorus to keep their lungs and heart and muscles working.  They will not crave additional Ca & Phos that could improve milk production or aid with conception.
To me, the most important part of a mineral (whether loose, block or tub) is the trace mineral and vitamin levels.  These have a huge impact on reproduction & health (both the cow and the calf) and their availability in home grown feeds and pastures are questionable at best.  Cattle will not crave missing trace minerals or vitamins - they'll just go on doing what cows do and maybe not get bred, or wean a lighter calf, or live a shorter life.