By default the BitBox02 comes with one (1) complimentary microSD card, on which you will by default store a wallet backup when first setting up your your BitBox02.
You can use additional microSD cards to create more wallet backups or write down your 24 recovery words.
In general, having multiple backups is better than having one, which is much better than having none.
However, keep in mind that a wallet backup gives complete access to your wallet (unless you are using an optional passphrase) so make sure that all of your backups are stored in secure locations.