This plugin helps the users to view your blog in a pda and iPhone browser.
Yes. These days lot of people are using PDA and iPhone. Making your blog mobile friendly is no harm.
Not needed. You have to just upload the files
If you want to disable the iPhone beta template please remove the word iPhone from user agent in PDA options page.
No. This plugin uses some of function of wordpress. WordPress has nothing to with plugin. So de-activating this plugin is 100% safe.