I'll tell you what the bumps and slides mean to me.
Dramatica is a VERY logical and objectified view of story. It presents a way to analyze and structure stories in a manner that allows me to build stories like I might prepare a cooking recipe. It gives me categories of ingredients, procedures, order of preparation, etc. What is does NOT do well is give me the FEEL of the story (a view almost exclusively that of the audience).
The bumps and slides logically indicate to me what I can FEEL is going on in a story when I view it. It provides a fairly concrete connection between how the story is put together logically, and the feel of it when experiencing it. So for me, the patterns of the bumps and slides helps me connect the way I want the story to feel (or not feel) with the overall structure of the story. This gives me a general ideal of how my story may play with an audience.
For example, the Z-pattern (bump-slide-bump) explains the FEEL of a traditional three-act story BETTER than the three Journeys Dramatica uses. It does not negate the value or use of Journeys, it just explains the feel of a story more accurately than the explanation of Journeys ever did (which is one of the reasons I continued looking for other explanations in the first place.) Secondly, I can use the "feel" of the story an another standard of measure when I analyze a story. If it feels like an episodic story but is structured like a z-pattern, then that might indicate I should recheck some of my storyforming choices--as well as look to which throughlines are emphasized and which are not.
The short answer is that bumps and slides give me more ways to understand what goes on in a story, whether I'm creating one from scratch or analyzing a finished work.