Levels are something that should always be watched, and when you have vocals with a huge dynamic range, constantly tweaking the level with automation gets to be a real pain. Waves has released a vocal rider plugin which helps try to even everything out without having to manually write in tons of different volume automation. It's an extremely handy plugin, despite it being simple in operation. The plugin has quite a few features for being such a simple plugin. Aside from the main sliders of range, vocal ride and output, it also has knobs for vocal/music, a switch for fast/slow and a few other small features that really help shape how you want the vocal rider to function. To use this, simply enable it on whatever vocal buss(es) you have and set it. You generally want to put all the vocal busses into one master aux buss and put this as close towards the last plugin. I never read the manual, but this is so easy to use that it shouldn't be needed.
Waves plugins have always been some of the most stable plugins I've experienced. They're cross platform compatible, so they'll work with both PCs and Macs. As a Mac user, that's a huge advantage for someone like me. They run in 32 bit mode, but Logic uses a wrapper-like application that runs so you don't interfere with your 64 bit interface. I've tried this on various different buses, and it seems to work on anything with ease. It even works nicely on MIDI, which I found a bit surprising. There are no performance issues at all, and that's a huge plus when working in a DAW filled with all kinds of synths and tracks running tons of plugins. These plugins came with my Mercury package, and I've had that for a few months now.
With today's metal vocals, you tend to find a mix of singing, growls, screaming and other types of styles mixed in. It can be a real pain to constantly adjust all of those levels manually, and I've found that this plugin can help quite a bit. When things get very extreme, I find that it can sometimes be a bit odd, but it could just be me dialing it in incorrectly. Regardless, it's a very good plugin that I've used quite a few times before to help level everything out.
The Waves Ltd. Vocal Rider was an easy plug-in to install (as is usually the case with Waves plug-ins) as it was straight forward and took about as long as it usually takes to do a basic install of a plug-in. While I not completely convinced that this is a necessary plug-in to have, it does have an easy enough to use interface. You've go three sliders - one main one labeled 'rider' to control the vocals in a mix and two others for range and output. It also has knobs for vocal, music, and another slider for sensitivity. It also has automation options on the bottom of the plug-in. I haven't seen a manual for this plug-in, but I don't think that you need one as it is easy enough to use on its own.
I've never had any issues trying to run Waves Ltd. Vocal Rider as it doesn't take up much processing power at all. I have used the plug-in on an Apple G5 desk top that runs with a Pro Tools HD system. The plug-in has always run smoothly for me whenever I have wanted to use it, which hasn't been all that often since the first time I used it. Even if you are running this on a Pro Tools LE system I don't think that you'll have any issues running this as long as you have a system that can run other plug-ins. It really depends on your system and how well it can handle plug-ins.
To be honest, since I first used the Waves Ltd. Vocal Rider about a year ago I have only used it a few more times as I just don't think that it is necessary. I can do exactly what it does without the plug-in and don't think that it saves me enough time to warrant using it. I didn't have to buy the plug-in as I have used it at a studio and I don't think that I would buy one and use it otherwise. While I can see why people will find this helpful, for me it gets in the way more than anything. I don't believe that it is worth the price but would encourage those interested to try it out to see if it will be helpful for them as every engineer likes to work differently...