Getting the right gearing setup for your individual circumstances is important to how enjoyable cycling can be. I'm getting old, tubbyer than I'd like to be and insufficient leisure time to get particularly fit. Combine this with very little flat ground, an interest in getting off the tarmac and the need to haul 30 kg of groceries on a Sunday morning and gearing range has become a key criterion for me. This means wide range cassettes/freewheels (e.g., 11-42 10-speed, 12/13-34 7/6-speed etc) and chainsets (51-41-30, 42-33-22 [150 crank - gain ratio], 46-26). Very little of this is available out-of-the-box so fettling and friction-shift skills are useful. I prefer the triples and see them as 1-bys with options. The wide-range double provides the range but requires a very different, and more taxing, approach to shifting patterns. A 1-by with 15% gaps would need to be 15 or 16-speed to achieve the same range.
If I lived where gradients were shallow and flats extensive then all this would change.