Driver voltage spread narrow or wide which is better?

I’m searching for various budget drop ins to fit my SolarForce L2 series. However, i have learned that the cumulative battery volts must match the drop-in (driver?) or bad things will happen. One of the things that drew me to the Solarforce line is I can use a variety of batteries, and battery groups in the same host/configuration. I can use a single CR123/RCR123, two CR123/RCR123’s, a 18650, 3 CR123’s or 2 18650’s. Except for the single CR123/RCR123 I can use the same SolarForce XM-L2 U2 drop in because it has a volt spread of 2.7-9V. The SolarForce drop-in for the single CR123/RCR123 needs a lower volt range. (The SolarForce drop-in that is available is a XP-G R5 0.8-4.2V). But in searching for alternative drop-ins I notice that many have very narrow Volt spreads, 2.7-4.2V. So why do different drop-ins have different volt spreads? Is one spread better than another, narrow or wide? What are the pro’s and con”s of each type?

My thread is already useful! :smiley: