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On https://www.emacswiki.org/emacs/MultilineRegexp one finds the hint to use
[\0-\377[:nonascii:]]*\n
instead of the standard
.*\n
to match any character up to a newline to avoid stack overflow for huge texts (37 KB). Is the overflow the concern here, or is a matching run for the former also more performant than the latter?
In Emacs's regexps, . does not match all characters. It is a synonym of [^\n]. So the reason for using [\0-\377[:nonascii:]] is when you want to match "any char, even a newline".
W.r.t overflowing the stack, .*\n should be handled very efficiently, i.e. without backtracking and without eating up the stack. On the contrary [\0-\377[:nonascii:]]*\n is handled rather inefficiently by Emacs's regexp engine because it will eat up a bit of the stack for every character matched, so on "huge" texts it will tend to overflow the stack.
Note that the emacswiki suggests [\0-\377[:nonascii:]]* and not [\0-\377[:nonascii:]]*\n.
[\0-\377[:nonascii:]]* would do so less then \\(.\\|\n\\)*. So I think the emacswiki is wrong on this one.
| might need more backtracking, but whether it actually does depends on how it's compiled.
[\0-\377[:nonascii:]]* (which is rather unusual, since you might as well use point-max rather than search for it via such a regexp) (for the curious: the crux of the matter is whether the set of chars that can match after the * is disjoint from the set of char that can match within the *. If it is disjoint, then the regexp engine will skip recording intermediate steps, and hence avoid eating up stack space. So .*\n and [^a]*a don't consume the stack, whereas .*a does).