It has to be said some horses love thier lick, but plain salt should be found naturally in their diet.
If you are doing lots of fast work and causing them too sweat a lot then I suppose it is a good idea to have one about the place to replace lost salt.
Naturally horses wouldn't do lots of fast work every day.
Mineralised ones can be useful if you, like us, suffer mineral shortages in the land. We have a terrible copper and cobalt and selenium deficiency, even our sheep get copper enriched mineral blocks.....which is unheard of south.
Added minerals is the only reason we give them because the land is constantly being drenched by the sea where we are.