The filter in Reports and Analysis updates the totals once you type in something on the filter and hit enter. However, in Analysis Workspace this does not get updated. Let's say I have a list of sections on my sight and one of them is called "Training". let's say I have 1,000,000 page views for my whole site and 250,000 for Training. Training would then consist of 25% of the totals overall. If I filtered for Training in Reports and analysis then it will update and say the total is 250,000 page views but if I filter in Analysis Workspace then it still shows the same totals. This is just a very simple use case to convey the idea.
I have found that i can create a segment and place it in Analysis Workspace and it will update the totals but it would be really helpful if I didn't clutter my segments by being able to filter like I can in Reports and Analysis.