Electrum's focus is speed and simplicity, with low resource usage. It uses remote servers that handle the most complicated parts of the Bitcoin system, and it allows you to recover your wallet from a secret phrase.
Do not trust. Verify.
Electrum verifies that your transactions are in the Bitcoin blockchain.
Because Bitcoin is not about trust, It is about freedom and independence.
Main features are:
Safe: Your private keys are encrypted and never leave your computer
Forgiving: Your funds can be recovered from a secret phrase
Instant On: Electrum is fast, because it uses servers that index the Bitcoin blockchain
No lock-In: You can export your private keys and use them in other Bitcoin clients
No Downtimes: Electrum servers are decentralized and redundant. Your wallet is never down
Proof Checking: Electrum Wallet verifies all the transactions in your history using SPV
Cold Storage: Keep your private keys offline, and go online with a watching-only wallet
Multisig: Split the permission to spend your coins between several wallets
Add-ons: Electrum supports third-party plugins: Multisig services, Hardware wallets, etc