For years, I have been downloading high resolution imagery for specific jobs off of Earth Explorer. The newest imagery is often in single files with no single file covering an entire project. Perhaps there is a better technique, but in M8, I would open one image, then copy and paste-merge the other files into the first image to create a single image. I would then delete the single images from the map file to manage the impact of the project on our limited server space. (To answer the upcoming question why I have never used image servers is that in the past, they either didn't work, worked too slowly, or provided imagery that was not up-to-date.)
A recent project involved downloading 32 individual files to cover the entire area. In M8, meging 32 images would be a task taking a couple of hours and requiring saving the map file, exiting M8, and reopening M8 to free up system memory. I decided to see if M9 could do it differently. To my pleasant surprise, it does! The longest part of the entire process was loading up all the image files.
Now, I am really looking forward to the day when M9 can provide many of the daily image-producing functions I use M8 for.