Auto bucket size is the default option on the majority of pages. This dynamically adjusts your viewable bucket size to what is most relevant to your data set.
When viewing 6 hours of data or less, Auto will show you minute by minute data.
When viewing ~2 months of data or less, Auto will show hour by hours data.
When viewing 2+ months of data, Auto will default to a day by day view.
There is a pseudo "hidden" auto bucket size of 5 minutes. Your default load of a portal page will generally show 24 hours worth of data. With auto bucket size, this will default to a 5 minute bucket of data per data point.
This can be manually adjusted in most cases. So if 2 months of hour by hour data is too granular for your trend over time, feel free to adjust this!
Please see the below link to learn more about how to manually adjust this setting.