The array inside the angle brackets is a glob, (see perldoc -f glob) and while you probably could get away with using that for an array of alpha-numeric strings, things will behave much differently if there are any shell expansion metacharacters in it.

You probably will not get what you expect if you use anything more complicated than a single array of alpha-numeric strings.

use strict;
use warnings;

my @A = qw/a b c/;
my @B = qw/1 2 3/;

print "$_\n" for <@A,@B>;
print '*' x 10, "\n";
print "$_\n" for (@A,@B);
[download]

a
b
c,1
2
3
**********
a
b
c
1
2
3

So,

1. Yes it is documented
2. Yes, there are gotchas, especially if you are abusing it for the wrong reasons.
3. Yes, I have used globs in several scripts, though I used them for their correct purpose, not for their side effects