If I quote a group, I mean I want to quote the group, and I want it to look that way:
>> append [a b c] (1 + 2)
== [a b c 3]
>> append [a b c] '(1 + 2)
== [a b c (1 + 2)]
And if I append a block, I want it to be appended that way (it will be whether I quote it or not, as the quote is discarded under evaluation in any case.. though in modern evaluation, any quoted material doesn't have its binding affected.)
>> append [a b c] [1 + 2]
== [a b c [1 + 2]]
>> append [a b c] '[1 + 2]
== [a b c [1 + 2]]
This would only be obfuscated if blocks were a rendering trick for quoted groups... and it's not clear that quoted BLOCK! would be possible at all (or perhaps double quoted GROUP! wouldn't be possible).
And quoted blocks are useful (to this day, Red adherents don't understand what use a quoted BLOCK! would be, since they don't think of blocks as "evaluating".) But continuing the example above:
>> parse [[A] (A) [A]] [some ['[A] (print "Block!") | '(A) (print "Group!")]]
Block!
Group!
Block!
== [A]
And more generally, it's useful to be able to quote something when you don't know whether it's evaluative or not, and are splicing it into a stream of evaluation, if you don't want evaluation. Several sophisticated features in Ren-C and the API depend on the generalized ability to quote--even inert things.
For background... historical Rebol/Red doesn't have any general concept of quoting at all. It has LIT-WORD! and LIT-PATH!, that simply have the evaluative rule of producing WORD! and PATH! respectively. Calling a BLOCK! a LIT-PAREN! and rendering it with brackets certainly didn't occur to anyone at that time.