Revisions in WordPress enable you to go back and see what changed in previous versions of the post. 

However one needs to strike a balance, as keeping multiple revisions for each post is resource demanding. The flexibility that WordPress revisions give, is countered by the performance cost. Thus, we decided to allow 5 revisions (excluding the ones by auto-save).
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Please contact our support and open a support request if you believe your use case requires a different limit. We will investigate this and report back our findings.