It’s usually recommended to have at least two devices in case one of them stops working and you would like to use your funds or in case you, for example, lose your seed.
In the case of a broken wallet, you would be able to transfer the seed from the broken wallet into the second wallet, which would allow you to still be able to interact with your money. In case you would lose your seed, you would be also able to send all the coins to a newly generated wallet on your second device, which would ensure that their private keys can’t get compromised in that process.