It's often called "necking down". The connector is higher resistance, and will indeed have more resistive loss than the wire. It's a very small length, though.

It's often called "necking down". The connector is higher resistance, and will indeed have more resistive loss than the wire. It's a very small length, though. The extra heat is quickly dissipated into the the nearby wire through thermal conduction, so it will be only marginally warmer than the rest of the cable. This is a very common practice on PCBs. You can use a very wide trace where there's room, and narrow it to get around tight spots like between pins on an IC. When I built solar race cars in college, we optimized the powertrain for resistive losses over weight. We used 00 AWG wire from the battery to the motor, knowing it would max out at 40 amps. We would then "neck it down" to 8 AWG to go into 40A rated connectors. To a casual observer it definitely appeared ridiculous and wrong.