A Full Restore helps keep your Pokémon topped up in health as it removes all status conditions and heals you Pokémon’s health to full. You can get it after you defeat all 8 gyms. The only catch is it’s price; £3000. Therefore, you will need to save up quite a bit before you buy these in bulk.
When you finally have these, make sure you use them properly. Don’t waste them and use them at the start of the battle, and don’t waste them healing a status condition (in Pokémon Pearl, I have so much money I have 99 Full Restores). Make sure your Pokémon is low on health before using them, and don’t waste them on trainers which are not important. Keep them for the Pokémon League.