Hey folks--yes, I know, two liners and swithing sounds crazy but...hear me out. First, back country skiing is a broad church, and let it remain so. That's part of what makes these conversations so interesting...everybody's needs are different. Back to the two liner system...why would I ever do that? I generally do two kinds of tours: first, moderate tours with my wife, skin up toward some peak or pass or goal, maybe some scrambling or easy climbing near the summit, then down. Half-day to three-quarter day. We're nearly always with a guide on those days--I don't want to be responsible alone for managing all the risks with my wife. Time is never a pressure. I don't have to worry about weight at all. I can use a 1600-1800 gram ski, Shift bindings, hybrid boots, and so on, no problem, no stress, just fun. On those days, I'll just use a single liner, probably the overlap liner, because I like to make it easier for myself on the part of the day where I know I'll struggle the most, on the descent! The other kind of tour I go on is using my touring skis to access ice or alpine climbs in the Alps with climbing partners. Depending on the technical difficulty of the climbing route, you can put crampons on moderate-weight touring boots and they climb just fine, but as the technical difficulty goes up, it's really nicer to be in light touring boots, or touring boots with a really light and flexible liner, or real climbing boots. In the latter case, the packs get heavy, and you're changing into and out of boots anyway, so switching liners on the ski boots is no big deal. How would that work? Start in the morning with light touring boot and light tongue liner...approach climb...he light touurig boots and liners on, or switch into climbing boots if you're going that route...climb...come back down...put on touring boots with heavy overlap liner...ski out. The main advantage is that when you're skiing down, especially after a long day with a heavy pack, you have a solid boot/liner combination. It helps me feel safer and more secure. I'm happy to trade the small weight on the up and hassle at transitions for security on the down. But that's just me, for these uses. If I was repeatedly skiing up and down a peak or slope to get in as many laps as I could, I wouldn't use two liners. If I was a better skier, I would just make do with a thinner liner. If I was a better climber, I would just climb everything in ski boots. If I really had to be moving fast and counting every gram, I would go lighter, and so on. But, for my skill set and use, the liner switch solves some problems. I'd say that, if you're only going to make one transition during a day, it's something to consider. Afterall, people change socks, switch tongues in and out of boots (old Dynafits) and so on...sometimes it's really nice to take the feet out of the boots and let them breathe, air our the toes, and so on. Try it!