🔹 1. What does payable actually do?

• A function marked payable can receive ETH along with the call.
• A function without payable will revert if someone tries to send ETH.

Example:

function deposit() external payable { }   // can accept ETH
function ping() external { }              // cannot accept ETH

🔹 2. Gas differences

When you call a function:

• If it’s non-payable and you send ETH → the call reverts immediately. That revert still costs gas for execution up until the point of failure.
• If it’s payable and you send ETH → the call succeeds (assuming no revert inside your logic). No extra revert cost.

So it’s not that payable is inherently cheaper. It’s that payable avoids the revert gas waste when you send ETH.

🔹 3. Why does it feel more optimized?

Because in Ethereum’s execution:

• A payable function adds almost zero overhead to allow ETH transfer.

• A non-payable function adds an automatic check (require(msg.value == 0)).

  If you accidentally send ETH, it fails — and failure still burns gas.

So when you compare:

• Payable + ETH sent → works fine.
• Non-payable + ETH sent → fails, wasting gas.