Heal block is a move which stops the opponent from using moves like Moonlight, Recover, Softboiled. Wish etc. as well as the secondary effects of moves like Leech Horn and items like Leftovers - so it negates anything which heals the Pokemon who has been affected by Heal Block.
This move sees little competitive use, as very little movesets have the space to accomadate a move like that, and ingame you basically just need to bash your way through - so no it is not worth it for Latios or Latias. Especially Latios/Latias since they have such other good moves at their disposal.