BankAccount example. Why do we need balance in domain events?

[pdrolopes]

After completely reading the docs(thanks everyone for the work). I got confused regarding the balance value that is stored in each bank account event that withdraws/deposits some amount of money.

I would expect that the domain events wouldn't contain any balance value and that would be derived after processing all events.
Is there a explanation on why it is a better choice to add computed information in the domain event?