Parallels 7 from Bootcamp

I have a late 2011 15" MBP (Lion) with Windows 7 64bit installed using Bootcamp. I also own a copy of Parallels Desktop 7 from one of those Mac App Bundles but I have not set it up yet. I'm thinking of setting up Parallels to use with my Bootcamp partition so I can quickly access and use a few things on Windows 7 without restarting my MBP.

However before I do I wanted to first check to see what, if any, downsides there are to setting up Parallels. I'm not talking about the decreased speed when using Windows 7 in Parallels as opposed to Bootcamp but instead is there any slow downs to the whole system (such as boot time, shutdown time, etc.) even when not using Parallels? I vaguely recall reading that some people noticed a significant slow down in their Macs startup and shutdown speeds and possibly the overall speed of their Mac after setting up Parallels 7. Is this true? Is it just a possibility or a given? Is there anything to prevent it?

Again, just to be clear, I dont mean a slowdown when using Parallels 7 but an overall slowdown to the Mac (when in windows/bootcamp or Mac OS) just from setting up Parallels. Possibly due to changes it makes to the system and system files or something.?

I just don't want to end up setting up Parallels and then find my Mac running much slower and the only way to fix it is to do a clean install of Lion along with a clean install on Windows 7 on bootcamp. That would suck.

Any info you can give me would really help. Thanks.