Ohms matter because the lower the resistance (lower ohms) the warmer the vape will be. On a mechanical
mod, you can vape a much broader spectrum of ohms.....you can go much lower, for instance, than you can on a VV or VW mod because there's nothing to cut it off. But ohms matter a lot in the quality of the vape. They will also affect the amount of power that is required of your battery. If you're using a 3.7 volt battery, then if you like a warm vape, you might shoot for a 1.5 ohm atomizer or cartomizer or
rba coil (or even lower)...but if you like a cooler vape, you might like a 2.5 ohm atomizer or coil.
The voltage of your battery doubled, divided by the ohms of your atty or coil equals the wattage (output power) of your device, basically. So once you figure out what you like, you can sorta dial it in by changing the ohms of your atomizer/coil.
Trying to keep it very basic here.....but that's why ohms matter. Does that make sense?