It can be harmful to hold onto cards that don't help with instant melds if they prevent possible runs or sets. For example, if you have thrcaesar slotsee 7s and no other matching cards, it might be better to split one of them up so you can use the other cards in your hand to form a run. This flexibility is frequently what separates winners from losers. Any competitive card game, including rummy, requires a winning mentality.