Every time you increase the distance that is required for an extension cord to deliver the needed power safely and efficiently, you increase the resistance that the flow of power faces to get where you want it to go.
The response of the flow of electrons to not having enough conductors is the turn the flow into heat. The more the heat, the less the power that is delivered to the other end of the cable.
Even if your power need is only 25 feet from the nearest outlet, if you use a 100 foot extension cord, the electrons still have to flow over the entire 100 feet, lowering the voltage that is delivered to the device you are powering.
Harrison Bros. Inc.