Google Spider Bots Crawl Speed

Please let me have your comments how to set the crawl speed of google. Now I have the option to choose:

Normal or Fast

Also is there any disadvantages to change crawl speed from normal to fast?

Awaiting your comments.

If you server overloaded? I would set to fast unless you have any performance issues on your site that could make the extra hits or bandwidth consumption disadvantageous to you.

Thanks for your reply Joe.