the main issue is who owns your private keys and how safe the keys are. Think about it like keys to your personal safe. the concept at a high level is monetary sovereignty. The private key is used to access the coins that are associated to to a public address. so whoever has the private key of the address above, has a lot of coins!

As an individual, most likely you would want to buy a hard wallet such as a trezor (trezor.io) so that this device can store your key safely store your keys and therefore your coins.