(I'm neutral on this issue; I just want to open it for discussion.)
The original intent of the Formatting Sandbox was to provide a place for users to test out the formatting features of the Stack Exchange Markdown. However, recently, some users have been using it to test out bugs that break the view, cause the browser to freeze or crash, or exploit vulnerabilities in the browser. (Sometimes, the issues only happen in certain browsers.)
Should such answers be allowed? If not, should answers whose current revisions are otherwise fine but cause issues when displaying the revision history be allowed?
One reason for restricting such answers is that they deprive other users who want to use the sandbox for its original purpose from doing so. An argument for not restricting such answers is that the sandbox post is one of the only places on which those bugs can be tested without having to use a "real" post.
One way to implement this is to introduce a policy that any answer to the sandbox that anyone flags as causing breakage in their browser should be deleted without question. With the current system, a flag saying that "this answer causes breakage" may be declined if the mod handling a flag is using a different browser (which happens to not exhibit the breakage) from the flagger (whose browser exhibits the breakage). Again, I'm not proposing this to be implemented; I'm just putting forward one possible way with which the above can be done if the consensus is to restrict.