As far as i know you can also pay for certain services of the club with those official fan tokens, for example for merchandise or even for tickets and so on. If i remember correctly Lionel Messi also got a huge chunk of Paris Saint Germain Fan tokens as part of his signing back in August, which gave the whole fan token scene a huge boost.
I am also not really sure what the use-cases for those Fan tokens are besides an additional method of payment for certain services of the clubs. It just means you don't need a credit-card and therefore you don't need a bank to buy a ticket or other stuff.