This principal 3 killer-switche is designed by purism for privately and security.
I guess how and when you will turn it off?
The result may be so funny n interesting.
CB Cellular baseband
WB. Wifi Bluetooth
MC. Mic Camera
CB 20%off. 
I m not turn it off always
WB. 50%off. when I’m not use it
MC. 35%off when goto bed.
Bit hard to say without having had the device for X months to try it out and find out what approaches work well but …
I would say: WB off unless I am in a location where I expect to use WiFi, typically with the SSID and passphrase already stored in the phone. So if I am at home, WB would always be on. If I am at the house of one or two friends where they are OK with my using their WiFi then WB would be on. Otherwise WB would be off. (To use public WiFi I would have to turn it back on but using public WiFi is a bit risky anyway unless you are confident that everything you are doing is over secure protocols.)
It would be important to have WB off when in public areas like shopping centres, who will otherwise track you using your WiFi.
I don’t have much of an idea at this stage regarding the other two switches. I think probably CB on most of the time because, well, unfortunately that is the idea of a mobile phone. 
I have WB almost always off currently. Saves some energy.
GPS also usually off. Would have to be software-off on the L5 unless I want everything off.
Note that there is the possibility that at some point we could use the MC switch to accept an incoming call. It’s technically possible, but we need to see if it would be practical.
I’m planning to have MC and WB off unless explicitly required, and CB almost always on (I have too many old relatives who do not admit IP-native messengers - if not this, I would prefer CB off and WB on).
I’m not sure that this will be OK (how much time the software needs to detect the mic after switching on? If few seconds, it probably will be not very comfy to wait for these seconds on incoming call).
So, the time will show.
Btw,
Nice idea! Never thought about this.
All the more reason why we need an actual phone …
It may depend on where the kill switch cuts the mic - just the actual mic input or the ADC that processes it. If the former then could be near instantaneous. If the latter then the delay could be greater. All just speculation.
There could be many different new scenarios once you get these possibilities. In general I will have CB on all the time but for example in the ferry I could turn it off just to save battery. Also in certain places I could turn it off to stop snoopers tracking me.
WB will always be on when I am at home so that I can use our fast fiber network. It certainly will be off in the city where dozens of “public” services try to track you.
MC will probably be on all the time unless Caligas idea of using it to answer will work well in practice. But will the switch need to be replaced after some time because of mechanical wear ?
Based on some posts in Librem 13/15 forums, I’m not sure if I wanna use these switches so frequently. Apparently, even those who barely used them, had them crap out within 6 months or a year. I’m not saying that all were plagued with the issue, but it can’t be just a few neither. I know , that these are gonna be of different and newer design, but the concern is still there.
Of course , that’s a hardware side. All mechanical components easy to get problem. Many dust go in easy. The metal-contact loose inside the switcher. And the gap of switcher between with case will be drink. Remember iPhone earject drunk water etc…
At software I concern that what’s time response is reasonable from switcher off to on at run time apps. less half second (500ms) is preferred. Suppose two seconds(2,000ms) accept.
And other things is apps already set enable but the switcher off, what will they get. Go to no response (infinity loop) that’s the worst case.
Those are good questions but - until we have the phone, noone knows.