Given there are so many switches on the control panels, and they each served a specific purpose, was every single switch used during a mission to the moon (with the exception of the abort switch perhaps)?
Some switches were normally left in one position for the entire mission, and would only be changed in unusual situations.
One particular semi-famous example is the switch controlling the power supply for a module called the Signal Conditioning Equipment (SCE), which was necessary for sending telemetry from the spacecraft to mission control. It had two positions, NORM and AUX; it would be set to NORM to put it on the usual power supply. During the launch of Apollo 12, a lightning strike caused the SCE to glitch out. A controller suggested that the crew switch "SCE to AUX", which reset the SCE.
I can't swear that the SCE switch wouldn't have been toggled in preflight checklists, but I believe there was no reason to switch it in a normal mission.
Yes, there are a LOT of switches and there are a lot that aren't used during during normal flight; but,
- Some switches are only used for pre-flight and post-flight; but, they do get used.
- Some switches are used for emergency/exception conditions and unfortunately did get used (Ex: for Apollo 13).
- Since there wasn't much automation on Apollo, the astronauts did have to flip a lot of switches during the course of the mission.
If you are interested in more of the details on this, the Apollo Operations Handbook is available here. It lists all the lights and switches. Also, the Apollo 11 Flight Manual is also available here. It is a good example of what the astronauts have do do during a flight. It lists all the details of that were involved in the flight (including all those panel operations).
According to Wikipedia, one switch that was never used was the Standby Allowed switch for the guidance computer: AGC#Standby Mode
The standby mode was designed to reduce power by 5 to 10 W (from 70 W) during midcourse flight when the AGC was not needed. However, in practice, the AGC was left on during all phases of the mission and this feature was never used.
To add to Russell's answer, Ars Technica recently covered the Apollo missions and they had this rather interesting interchange about the "SCE to Aux" switch. It was really obscure, but NASA's "throw every failure at the crew" training system paid off. Even if every switch wasn't used in a mission, it was almost certainly used on the ground in training.
One of the brightest minds in Mission Control, John Aaron, sat at the Electrical, Environmental, and Consumables Manager (EECOM) console that day. From simulations, Aaron recalled seeing a similar pattern of nonsense telemetry data when the power supply to a piece of hardware inside the Command Module called the "Signal Conditioning Equipment" (SCE) had failed. Aaron deduced that switching this SCE box to its backup mode would bring it back online and begin transmitting correct telemetry data down to the ground. From this, flight controllers should be able to determine whether the crew of Apollo 12 were flying a sick or healthy bird.
“Try SCE to Aux,” Aaron said. Although Griffin didn’t quite understand the significance of this message, he trusted his flight controller. The message was conveyed to the spacecraft by the CAPCOM, which was being run by astronaut Gerald Carr.
“FCE to Aux?” Conrad replied. “What the hell is that?”
“SCE, SCE to auxiliary,” Carr told him again.
Alan Bean, sitting next to Conrad, recognized the command and flipped the switch. Almost immediately, power came back on to systems within the spacecraft. Mission Control began receiving good telemetry data.