The power is yours!
Well, as much as it can be anyway. You have the power and knowledge to customize capabilities, dashboards, reporting, and more through custom-built web applications that are hosted internally on Marketing Cloud and used inside the Marketing Cloud UI. With this power, you could build things such as a NoSQL segmentation tool that can programmatically create often used queries in your account without the user needing to know or understand SQL. Or, build a custom reporting dashboard or tracking log based on data you get via API or other scripts, and so on for your users to easily digest.
There are so many possibilities here that it is hard to list them all. Now, the thing to also keep in mind is that although in our example we did this completely in Marketing Cloud, you are not limited to that.
You can host these applications externally, but you would no longer be able to use SSJS or AMPscript and would instead have to utilize another language to interact with...