What is the difference between 'will' and 'be going to' based on the text?

According to the text:

• 'Will' is used for on-the-spot decisions, requests, and predictions based on opinion or imagination.
• 'Be going to' is used for plans.

The text provides examples for 'be going to': 'What are you going to do?' (indicating a plan) and 'We are going to go swimming.' (a planned activity).