It means that it's better to have something tangible to use, that you can hold, physically see and touch than to have it out of your reach. For example, it's better to have $10.00 in your hand, than $100.00 that you "might" get.
What is meant by "a bird in the hand is worth two in the bush"?
Sometimes one can solve 2 problems with one solution at the same time
It means to have got one for sure than to have two possibly.