But a second SIM slot isn't just an advantage in terms of savings. People with work phones, for example, could benefit from the availability of a secondary slot as they'll have to carry and worry about charging one device less. And even if neither of these reasons mattered to you, having the option to pick an additional card down the road if the need arises can be seen as an advantage.
So say a version of your smartphone was available with two SIM slots, but costs $10 more. Would you prefer it over a standard, single SIM model?