There is really no difference between a "sweep" and a "send"... both create transactions that transfer coins from one place to another.
The "sweep" functionality is just a convenience function that enables you to send directly from a private key without first importing it into your keystore... Basically it just does this:
- Locates ALL UTXO's for address associated with given private key
- Creates a transaction that sends total value of all found UTXO's to new address specified
- Signs transaction with given private key
- Broadcasts the transaction
You can do the same thing by:
- Importing your private key into "Offline" Electrum
- Importing your address into "Online" Electrum (This finds all the UTXO's)
- Create transaction on "Online" Electrum that transfers ALL the UTXOs to the new address
- Save this "unsigned" transaction
- Transfer "unsigned" transaction to "Offline" Electrum
- Sign the transaction with private key in "Offline" Electrum
- Transfer "signed" transaction back to "Online" Electrum
- Broadcast "signed" transaction
Both methods effectively do the same thing... just one is slightly more time intensive