Unsigned Transactions vs Signed Extensions

Question

It seems that I can use a signed extension anywhere I can use an unsigned transaction.

Can you please explain why I would implement one over the other?

How does the transaction lifecycle differ?

The only reason I would imagine I would use an unsigned transaction would be when the submitter does not have an account.

Answer 1

Have a look to Bruno's answer here. It covers both rationale and transaction lifecycle for unsigned extrinsics.