[WernerF]

I agree that it's best not to print your plugins effect by going through an aux with the plugin on it. I do, however, think that it is highly beneficial to "mix as you go" in order to have a sense of what your track needs in the form of overdubs. This often require's the use of plugins which, of course, you only need to monitor through. It also serves to inspire the players that are performing the overdubs. I used to, as a session guitarist, play on tons of other peoples records and if the engineer or producer had not made the effort to make the track sound as inspiring as possible it made it quite difficult to deal with creatively. A little extra work goes a long way.