Your user data on your hard drive is encrypted (and MACd) to prevent unauthorized reading, and to detect modifications. Latter part means an attacker could wipe your whole disk and write own stuff there, but replacing single files etc. with something sane is not possible.
If /boot is encrypted too ("if", because many instructions leave /boot unencrypted), what for? To prevent reading Grub (it's a known software)? No. To prevent malicious modifications? Maybe, but nothing stops me (let's say I'm the attacker) from overwriting the "whole" Grub partition with my own malicious bootloader (or supply a second disk with an own bootloader). I don't know your own files, but I know how to make a /boot partition. ... Meaning, you lost. My own bootloader can take over the computer as soon as you turn it on, and spy on your HDD key later.
About GRUBs configuration console, preventing access without password does make sense in a specific situation: The attacker can not access the hard drive. Think ATM. (If he can, as said above, the password is useless too.)
Similar for your UEFI settings password: If I can access the hardware (replacing mainboards, flashing chips, ...), it's completely useless.
Bottom line, what do you want?
Protect your files from being read, but if your computer gets stolen you can't ever trust it anymore (even if you get it back)? Keep the disk encryption, and ignore the rest.
Protect your computer from being stolen and/or modified? Use all and put it into a safe, with a radiation shield and much more.
Somethine else? Impossible.