You can also use Delete if you do not plan to archive e-mail pieces. Once you introduce a topic into the incremental reading process, it will come back to you sooner or later. You should rather use tasklists for elements that are not in the review process to review them starting with the top-priority pieces. If you experience an e-mail overload, keep the lower priority pieces on the tasklist and introduce them into incremental reading gradually starting from the top. Consequently, if you import an e-mail today, the earliest incremental review will come tomorrow.
Random test is invoked only then when there is no material scheduled for today.