Hhhmmm... This is usually a subject I get into with coil builders but the principles hold for drop in coils, you just have less room to maneuver.
If you hold the coil size, wire size and resistance constant, when you change wattage you are adjusting the amount of power radiated from the coil surface, and the surface temp of the wire. Some people like their vape cooler, some warmer. Some juices perform better in certain power ranges; particularly those with complex flavor profiles. Not enough power and you lose certain highlights that don't get hot enough to fully vaporize; too much power and you can lose highlights that burn off instead of vaporizing. Some wicking materials keep up just fine at one power level, but fall behind if you raise it too far. Moreover, it is possible (actually inevitable) to build two coils of the exact same resistance using different sizes of wire and get different radiated power at the same watts. Smaller wire gets hotter (ratio of surface area to volume is smaller) than bigger wire, all else being equal.
So, as you can see, there's a lot of variance here, and many things are interdependent; like Ohm's Law itself, if you change anything, everything else moves to stay in equilibrium. There really isn't a "preferred" wattage setting for any given coil value because they can be built in different ways. A Clapton coil and a round wire coil and an Alien and a twist and any other permutation you can think of, all built to the same resistance, will "behave" differently at the same wattage because you are changing the ratio of surface to volume. As the word itself says, it's about personal preference, not some absolute rule, and the key to a satisfactory vape is finding a surface power level you and your juice both like.
So you get the same advice from me as from everyone else: start low and work up until you get where you want to be. Be further aware, if you like to change flavors, some juices will like certain wattage ranges and others will like another. Seriously, just a couple of watts in one or another direction will make a difference in the flavor profile. But only you can tell when it's right for you. So play around with it: pick a coil and a juice and run up the power to get in the right area. Then vary the watts just a point-- half a point, even-- up and down to get it dialed in perfectly. The repeat the process with any other juices you like to use.
