Like the undo in word, this could undo 'stpuid' actions. This that are difficult to manually re-ajust, this could unmerge tickets, or restore a deleted client, invoice, or ticket. Unblocked a blocked ticket (you realise you blocked a client in the spam protection).
I realise this could be seen a as stupid proof fetaure and may take alot of integration, so just wondering what other people think.
I don't think it should be easy to undo, just have the ability, in other words. help > undo "Please fill in your password" This is what will be undone "delete client x".