No unlike the desktop wallet both our mobile wallets are HD (https://en.bitcoin.it/wiki/Deterministic_wallet) this means that just a single backup (or just the recovery phrase) will always be sufficient to keep your money safe, the wallet is able to regenerate/recalculate all used addresses from an old backup even if you have generated millions of them since the backup was made. That said in such an instance you will still lose other transaction history information (like labels and whatnot) if you recover from an old backup, so there are still benefits to frequent backups - but is not as important as the desktop wallet.

What is very important is that you keep the recovery phrase and/or a single backup copy somewhere safe so that you can always recover and keep in mind that if the recovery phrase is stolen/compromised it can be used to steal your balance (so its important you keep it in a safe way - the wallet backups are encrypted with a password of your choice to help facilitate this)

With the desktop wallet (and this applies for pretty much all coins) backups are good for (roughly) 100 new addresses - so you also don't need to backup after absolutely every transaction but it is good practice to do so regularly. If more than 100 addresses are allocated since last backup then you can lose money when restoring from the old backup - we will likely do something to make this process more friendly/safer in a future release.