What's the difference between linking more than one calendar and integrating more than one calendar account?
One calendar account can hold any number of calendars. They can be your own (e.g In Google Calendar they are listed under My Calendars). Or they can be shared with you (e.g in Google Calendar they are listed under Other Calendars). As long as the shared calendars are shared at the level of 'make changes to events', then YCBM will be able to see them and add appointments to them.
So, if you are trying to work with a colleague's calendar, for example, they will need to share their calendar with the correct permissions for it to work. Or, you can integrate a completely separate calendar account, with all of its own and shared calendars. This might be a better option for individuals who don't want to share their calendars. Find out more about working with multiple calendars.
Note: The pricing is based on the number of calendars you link to under the Calendar & Teams page. You can integrate with as many calendar accounts as you need. But the price is based on the number of calendars within the calendar account that you are using. If you link to two calendars from one calendar account, then your subscription will be $20 per month.