Some mainboards still have 20 pin ATX power connectors, while some
boards have 24 pin power connectors. Why is this?
Does it provide a performance boost? Like more power to to motherboard to use? More heat?
The 20pin power connectors are found on old motherboards and Intel Atom, just a change of standard. Almost all power supplies have a 20+4 connector however which allows you to use both 20pin and 24pin boards.
The gain is that the current draw on those lines is now spread out and reduces the risk of melting the connector. Its why some graphic cards have 2 pcie connectors instead of 1, One would just get too hot with all the current passing thru it.