Folks,
This is a very good and very valid question.
This is my 2cents.
High Ampere Hours (Ah) means not high current, it is the ability to provide the normally required current for long hours without draining the battery.
E.g. In Hilux (same case in Land Cruisers) if an electric winch is used, the battery should be able to operate it without draining the battery quickly. Also high Ah means the alternator is safe. Hiace Dolphin requires dual battery if they have dual A/C installed,unless the single battery will drain so soon.
Hope this helps!