Hmm. I think that what you're saying may not always be true, unfortunately. It _is_ true that you want all the gain that you need to get the input right up to operating level for the board at the very first preamp stage, so that all following stages (eq, summing amps, master fader makeup amps, and so on) are run essentially at unity gain. A great killer of the noise floor is to run the noise from one stage through 10dB of gain at the next stage, and 10dB more at the next, and on and on... You want to optimize the gain structure by getting all you need right at the preamp. But using _more_ gain than you really need, by artifically padding the mic signal before the input, strikes me as basically a losing proposition. More gain almost always results in more noise.
Mic pads are useful when you have a very high output mic, a somewhat low-headroom preamp, and a *very* loud source. As an example I used to be able to run my old
AKG D-12 kick mic directly into a line input: my kick style, and the output level of the mic, conspired to wreak _havoc_ with my mic pres. Couldn't turn the gain down far enough to handle the transients. I could have used a pad, but my thought was (and is) that fewer gain stages are better: less noise, less distortion. So into the line in it went, bypassing the pre entirely. Everyone was happy.
Mic pres usually have a sweet spot in their gain curves where their contribution to the overall noise of the signal chain is minimized. However, if you're really fishing down there *that* far into the noise floor, the inherent thermal noise of the pad (assuming an external inline resistive pad, and not a capacitive-divider pad inserted between a condenser capsule and the preamp/level shifter in the mic body) is likely to swamp any resulting minimization of the preamp noise.
All that's well and good, but that's also ancient history. Now, if you're using one of these newfangled boutique standalone preamps that colors the sound, and its coloration is a function of the gain setting, then maybe this is a valid technique: pad 'er down and crank the "color/gain" knob back up until you like it. Knock yourself out in that case. I don't do that sort of thing, myself. I'm a bit of a throwback, and want what little coloration is going to happen to happen right at the mic capsule. I want the electronics to pretty much leave the signal alone from then on. If you're working in a different style, then the rules will clearly be different.
Anyway, I always err on the side of minimum noise.
