Usually when you download an app on Google Play, you will be asked to grant certain permissions, such as access to contacts, use of your camera, access to sms, etc. in order to use the app.
The app needs this permission to make certain features work, and thus, it requires it in advance. Your app, however, won't perform any operations automatically in the phone with this permission unless you use related features. For example, the Whova app won't access or change your contact information unless you explicitly export one contact into the phone using the business card scan feature.