One of the big differences between dedicated assistant services like Zirtual and on demand services like FancyHands is the ability to do recurring tasks. A dedicated assistant gets to know you and you'll always be dealing with the same person so for instance, you can say "Do this every Monday..." you can definitely tell an on demand service to do the same thing each week, but each week you'll have to assign the tasks. Some might see this as a limitation but I actually see it as a positive.
Regardless of which service I use to accomplish a repetitive task, I like to use Resnooze, a service that simply sends you recurring emails at whatever interval you choose. I have several repetitive tasks each week, such as putting up my Succulent Saturdays, Top Task Tuesdays, and Solution Sundays posts, as well as things like dealing with the very small amount of paper I get each week.
I get the email with my well explained task description and I simply forward it to the right assistant service. I like doing this for a couple of reasons. First, it allows me to stay somewhat in the loop on these important tasks, it also is a reminder to me if I need to have any input on the task (such as creating content for a blog post). Finally, whether it's an on demand assistant who needs to be instructed for the very first time, or my regular assistant who wants to make sure they don't miss a step, it ensures the task is done properly.