I've wondered about this for a while. I'm old, slow, and heavy, so I've got gears down to 20 gear inches on all my bikes, even the one without racks, so I can climb some ridiculous hills when it's hot and I'm tired. But some people recommend doubles for touring with light loads. At what point of youth, fitness, and light load does a 27-30 gear inch low become a viable option for touring?
Triples are still widely available in touring and mountain bikes, but are getting less common in regular road bikes (the kind you need for lightweight touring). You can get a road bike with a compact double and put a long-cage derailleur on the back and get your gearing down to 27 inches. That's enough for most lightweight touring.
I had a triple on my road bike until it got run over by a car. The bike I replaced it with only had a double. I expected that to be a big problem because I often ride up and down the mountains, but we humans, even old ones, are pretty adaptable. Even though my gearing isn't quite as low as it was before, I'm fine with it.