For final edits on a presentation I take advantage of dual monitors, with PowerPoint on one screen and the slideshow on the other. As I adjust elements I can see the updates immediately.

If you do not have a dual monitor setup, you can do something similar by running the presentation in a smaller window by holding down the CTRL key while clicking the SLIDE SHOW icon in the lower left. You can move back-and-forth between the slideshow and edits while seeing the updates immediately.
CTRL + Click to start show in window

Troy @ TLC