Doubt with geting data from excel

Hello,

I'm preparing myself for the certification PL300 and I have a doubt regarding to the information I found in the documentation :

1. If we get data from local excel file, I undersand that changes to the original excel ARE REFLECTED in Powerbi after refreshing Powerbi. So I don´t undersand why it says that we should use it for data that doesn´t change. If we put updating data in service every hour, it will update it. 

2. If we get data from excel of onedrive, it says that reports are automatically updated. 
I created a powerbi report with data loaded from WEB -> onedrive ( I put my URL there). 
Then I published that in service ( the same account in Onedrive as in Powerbi), I changed data in excel in onedrive, and my data doens´t change automatically in Powerbi.
I have to put " refresh" in Powerbi to see data changed. 

The documention says that OneDrive and Powerbi connect to each other about once an hour. 
so I it refreshes it automatically. 

So, why if it is automatic, why do I need to refresh PowerBi ?

I don´t get what the documention says. 
Can you please help me to understand that?