What are the specific differences between client 300 and client 400?

Hi.

We have an S/4 HANA env based on SAP S/4 HANA 1809 FPS02, Fully-Activated Appliance.

I would like to know what the specific differences between client 300 and client 400 are. Please let me know!

I know the below information.

-300 Best Practices reference client(whitelist approach)

-400 Best Practices reference client(merged-000-client approach)

-And I've already read the following doc.

https://help.sap.com/viewer/S4HANA_1809_AdminGuide/17d958a88d244ee293aed687f9bfe37f.html

However, I couldn't understand what the specific differences were. tables, records, settings,,,

I would like to choose a client to evaluate functions ether 300 and 400.

I plan to select 400. Is it suitable?

Thanks in Advance.

Best regards.