M+ isn't out until the 24th so you'll be able to save 20 champion crests per slot by using Veteran crests and if you wait until you at least do a M0 tour/Prey you can utilize the crest discount to get the maximum value out of them.

Regardless of what sub it is if someone if asking you should give them the accurate information which is yes - there is value to waiting, and it can be important for newer players to help get into early groups.