We believe that our customers should own their data, and that belief is in the core of this important feature.
Funnel uses Gmail or Google Apps first of all to handle your identity within the service. Also to store all conversations and contact information you create through Funnel, that way even if you decide one day you don’t want to use Funnel CRM anymore you don’t even have to mess with exporting your data, and migrating it elsewhere. It stays right there, in your Gmail account where you can continue any conversation you had with your own customers, and all your contacts are conveniently at hand.
Once you sign in with Gmail, you are actually signing in (or creating your Funnel CRM account if you're signing in for the first time) through Google's oAuth service, and you are granting Funnel access to your emails and contacts.
This is absolutely necessary for Funnel CRM to work, although we are only requesting access to your identity (name, email address, and avatar), and not access to your inbox and email messages.