Why was salt so important to Roman soldiers?

It is sometimes said that the soldiers of the early days of Rome was paid with salt. This is because their pay was called salary, which is purported as being derived from the Latin Word for salt. However, there is no evidence whatsoever that this was the case. It is more likely that they were paid in money from the outset. They might have been given salt rations to give to their relatives because at time of war salt prices rose. Salt was a very important commodity up to the invention of freezers because it was used as a preservative.