Here are the permissions Gonebusy asks for and the reasons why:

Confirm your identity on your workspace
This is a basic permission for all Slack apps in order to verify your user information and that you are authorized to add the app to your Slack workspace.

Add slash commands and add actions to messages (and view related content)
This allows Gonebusy to install the /gonebusy and /today slash commands as well as attach custom actions to any message.

Send messages as Gonebusy
This installs the @gonebusy bot that you can invite to channels, as well as speak to in a DM channel.  When you talk to the bot or request slash commands, the @gonebusy bot reply or post message to you.

View email addresses of people on your workspace
Gonebusy uses the email addresses of people in your workspace in order to create and manage attendees properly for your Google Calendar events.

Access your workspace’s profile information
In addition to your Slack team members' emails, Gonebusy uses the full names and timezones found in your workspace's profile in order to seamlessly communicate on your behalf with your fellow Slack team members.  
This permission is also required in order to receive notice from Slack whenever a new team member joins your workspace.  The newly joined team member will immediately be available for invitation to bookings you create with /gonebusy or by talking to the @gonebusy bot.

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