Today's Marketo instances aren't managed by a single admin user. In an ideal situation there are different users with different permission levels each managing their own operations inside Marketo.
While this situation is fantastic as far as distribution of labour and ensuring that you can get the most out of the system goes, it makes the role of the Marketo administrator infinitely more complicated.
It'd be great to be able to see usage information such as which users have been active and what they have been doing.
Particularly when working with a large organization, the ability to monitor users activities would provide a phenomenal boost to the admin's ability to provide oversight and simply to ensure that users are utilizing the tools provided to them as intended.
In addition, it would help the admin know where they need to reach out and how they can help, and having that visibility into users activities would really help in those cases where you receive late night phonecalls saying "I've broken it!"
The addition of an edit log is well overdue, because today aside from Created and Last modified, we know nothing about the modification history of programs, making understanding changes created over time nigh on impossible.
With the addition of a few simple tools, managing a broad Marketo implementation would be infinitely less complicated and it would definitely improve the lives of the primary admins.