The installer requires that the EFI partition have a capacity no less than one
half gigabyte. In practice, the GRUB bootloader files consume about one percent
on this capacity. Since resizing the boot partition is cumbersome, it is
helpful to allocate a generous capacity, in excess of the expected need, but
the present requirement is extreme. Installers for some OSs enforce a minimum
of one quarter gigabyte, and even a capacity so high seems extreme. Unless a
system is to be loaded with utilities from the hardware vendor that would run
in the EFI environment, usage requirements exceeding 100 megabytes would be
extremely rare. 

It would be helpful if the installer imposed no lower limit on the size of the
EFI partition, although a warning against a very small size may be appropriate,
for example, recommending but not enforcing a minimum of 100 gigabytes. Many
may choose an even smaller size, without ever regretting it.