Why you have to be careful using versions in Mongoid

Mongoid Hierarchy Excerpt

Mongoid/Hierarchy

# Get all child +Documents+ to this +Document+, going n levels deep if
      # necessary. This is used when calling update persistence operations from
      # the root document, where changes in the entire tree need to be
      # determined. Note that persistence from the embedded documents will
      # always be preferred, since they are optimized calls... This operation
      # can get expensive in domains with large hierarchies.
      #
      # @example Get all the document's children.
      #   person._children
      #
      # @return [ Array<Document> ] All child documents in the hierarchy.
      def _children
        relations.inject([]) do |children, (name, metadata)|
          children.tap do |kids|
            if metadata.embedded? && name != "versions"
              child = send(name)
              child.to_a.each do |doc|
                kids.push(doc).concat(doc._children)
              end unless child.blank?
            end
          end
        end
      end