What does "one request at a time" mean?

You can queue as many requests as you want. However, we work on one actively at a time: that's what guarantees quality and real follow-through, rather than ten rushed projects in parallel.

As soon as a request is delivered and approved, the next one in your queue starts. You stay in control of the priority order at all times.

Both plans work on one active request at a time. The difference with Pro+ is not throughput but priority: Pro+ requests move ahead in the processing order.