This never really got answered, so I thought I'd have a go. The difference between low resistance + low wattage and high resistance + high wattage is an awful lot of heat. Lower resistance coils are usually used with higher wattage, which lower wattage goes with high resistance coils.
With a mech, you will have been using the resistance (ohms) as a sort of power control - lower resistance for a hotter vape and higher resistance for a cooler vape. Regulated mods don't exactly work that way because you now have the ability to control the power directly. If you want a hotter vape, turn it up; if you want a cooler vape, turn it down.
Resistance does still matter, but it's mostly indirect. Assuming you're using simple wire (not twisted or claptons or other fancier builds) it works like this:
Resistance depends on:
- The material a wire is made of - kanthal, stainless steel 316L, or whatever else you're using
- The wire's gauge, which is a measure of its diameter. Higher gauge wire has a smaller diameter, so it's thinner. Lower gauge wire is thicker, with a bigger diameter. The fatter the wire, the lower the resistance.
- The length of wire in your coil. This is a factor of the coil's ID (inside diameter) and the number of wraps. Shorter wire = less resistance; longer wire = higher resistance.
Say you build a coil of 24 gauge Kanthal A1. 5 wraps at 2.5 mm ID would give you a coil of about 0.43 ohm. Now you want to switch to MTL, so you want a higher resistance coil (usually). There are two ways to do it. You could add more wraps and/or increase your ID so you're using a longer wire for your coil. 8 wraps of 24 ga Kanthal A1 at 2.5 mm would give you 0.66 ohms.
Or you could switch to a thinner wire. 5 wraps at 2.5 mm of 26 gauge wire instead of 24 gauge wire would give you about 0.64 ohm.
Those two coils would have almost the same resistance, but they'd behave very differently and would need different wattages to power them, mostly because the 24 gauge one has an awful lot more metal in it than the 26 gauge coil. Steam engine suggests 32 w for the first coil and 16 w for the second one (actually, Steam Engine doesn't recommend making the first coil at all - it has too much metal and would take too long to heat up and cool down).
If you want to learn more about what combinations of gauge and coil size are likely to work well, I'd suggest checking out
Steam Engine's Coil Wrapping page.