Topic probably says it, and I don’t know if my walls have them right now, but what is the purpose of the neutral wire? Sounds like it’s not used normally but is for most smart home devices? Yet somehow Lutron and Monoprice switches do not need them?
Let’s have a guess you are talking about wall switch positions?
For a mains powered device, you take current flowing between live and neutral wires for your power.
For an old fashioned bulb, you only need a live-in and live-out at the wall switch. The neutral wire can go direct to the bulb and save wire, while the bulb takes its power from live-out from the switch and neutral.
When you put electronics at the wall switch, it needs to be powered as well. Now you need a neutral wire, for the small amount of power the electronic switch gear needs.
Electronic switch gear that doesn’t require a neutral wire get’s its own power in a “cheating” way. When a switch is off, there is a potential between live-in and live-out at the switch. You can take some power from that by allowing a small amount of current to “leak” and eventually pass through the bulb and so to neutral. You can store that power up, like charging a small battery. Very often that’s enough to power the electronics.
Even when the switch is on, the electronics can “steal” a little bit of power now and again to keep its store charged. You shouldn’t notice a blip in the light of just a few milliseconds.
The neatural wire is always used, otherwise a device would not get power, it is sometimes just not available at the switch location. Sometimes the neutral is wired directly to the device and not sent to the place your wall switch is used and the switch only works on the active line. It is pretty common for it to be missing when a house has two way switches, that is when a switch is at both ends of a hall. One end may have the neutral but often the other end is missing. If building a house it is important to ask for it to be at 100% of the switch locations.
My house was 100+ years old and all locations did not have neutral.
As for how some devices state they need no neutral for switching is they source the neutral through the load, ie in the case of a old fashioned light bulb, the filament of the globe provides the return. There are cases when the load is different and will not provide enough return path for these devices so they usually have disclaimers in them. They also have other issues and it is always better to have the neutral.
Just one hint - please always switch the mains phase.
In some cases (e.g. if you can’t rely on the cable colors and you didn’t measure it) you could accidentally switch the neutral wire instead of the mains phase.
Meaning, even if you switch off your light, the socket will still have a potential of 230V (or other - depending on where you live).