I have some plugins from Air Windows, as well as saturation plugins (or any plugin that models actual gain staging in hardware for that matter) in which you want to have proper gain staging going into the plugin for the desired sound.
For example, I'm using Air Windows console, an encoder / decoder plugin in which you put the encoder as the last plugin on all your inserts, and the decoder as the first insert on your master: (more info here http://www.airwindows.com/base.html
) Lets say I have a REALLY hot synth pad that in order to get it to fit in the mix I have to throw the fader down to -22db (which is surprisingly common I find given each VI's need to impress when you load it up by playing back at insane volumes). If I put a air windows console as the last insert, which is still pre fader, I'm actually distorting the decoder part of console as when it adds up with all my other tracks, its WAY above 0dB. Of course if I had the ability to simply make this insert "post fader" nothing would peak as the fader is already at -22db to get it to fit in the mix.
I also find metering plugins make more sense post fader. Also, for limiter/maximizer plugins, having the ability to run them post fader is almost a MUST. For example, If you're drawing automation on a bus or master automation with a limiter, you may want the limiter to react to this automation "post fader" so you're not causing unnecessary gain reduction if the fader causes the signal to ultimately be under the threshold. Same could be true of compressors under certain mix conditions I would imagine. You can also do really cool reverb/delay effects with post fader inserts instead of having to use an aux track and automating it.
I know what your thinking, "just route the output of this track to a bus and now anything you put on the bus is post fader!" Well, this is true, but if your using console / tape emulation plugins on each track, and want these to be post fader, you'll run out of busses FAST! Plus it just seems silly to have to have add a bunch of buses in order to have post fader inserts, something that every other major DAW allows you to do directly in their channel strips! If every other DAW has them, they must have seen the importance / flexibility / connivence it offers, right? Cubase finds them so important that they use 2 of they limited to 8 inserts as post fader! Digital Performer even lets you have ALL your effects be post fader if you want!
Seems odd to me Logic doesn't have them at all. Sad to see they were not added in Logic X.
p.s. to get around some of these problems with the lack of post fader inserts I've been trying to use gain plugins, and while it works, I find it brings with it its own host of unfortunate annoyances. Simply having post fader inserts in the channel strip (copy how digital performer does this) would make life MUCH easier.