What type of Forecasts should you use when you enable Territory Management? Collaborative or Customizable Forecasts? When the features of both the Forecasts categories are similar, how do you decide which Type of Forecasts to enable, especially when you are using Territory Management?
Refer Territory Management documentation.
Original Territory Management is available only with Customizable Forecasts and is not supported with Collaborative Forecasts. If original Territory Management is enabled, you can no longer use Collaborative Forecasts.
The newer Enterprise Territory Management can’t be used with Customizable Forecasts. Enterprise Territory Management and Collaborative Forecasts can both be enabled and used at the same time in your Salesforce organization, but the two features are not currently integrated to work together.
So, it depends which version you are using Original or Enterprise version.