.* = "zero or more characters" = "there may or may not be stuff here"
(blahblah) = capture whatever is inside the parentheses so that it can be reused later
^investors/.*$ = ^investors/ The first form means "there might be more stuff between the part I've spelled out and the end of the test string". The second form means "it doesn't matter what comes after the part I've spelled out".
See how they're identical? The .* element is irrelevant unless you need to capture it for later reuse.
If you don't plan to reuse it, you don't need to capture it. If it doesn't have to exist at all, you don't need to test for it.
perhaps ^investors/ with no closing anchors means everything after investors/ e.g. investors/mymoney.php investors/index.php
Oh, you know what? You may be confusing mod_rewrite syntax with mod_alias (Redirect by that name). In mod_rewrite, nothing is reused unless it's explicitly captured and then named in the target. (Same pattern as RewriteMatch.) Redirect 301 ^investors/ http://www.example.com/litigants/ = "take anything that comes after /investors/ in the request, and instead attach it to /litigants/"
RewriteRule ^investors/ http://www.example.com/litigants/ [R=301,L] = "take all requests for anything in /investors/ and redirect them to the front page of /litigants/".
If you want to replicate the mod_alias (Redirect 301) behavior, you have to say RewriteRule ^investors/(.*) http://www.example.com/litigants/$1 [R=301,L]