Currently, filter settings (and sort settings) an on a per-tab basis (Folder tab, Search tab etc).
It is often requested that these settings should be on a per-view (per-list) basis instead, perhaps especially as regards saved searches. I totally agree with this, but:
In addition to this, though, I think it would be extremely useful also to have a global filter (or "pre-filter") - an overall scope or area of focus - that stays in place no matter how you switch between all the various views and list filter settings.
A good example of this is if you are at work. Then it would be useful to be able to set the "scope" (global filter) to "work", thus masking all other tasks in all views. This means you could use or "re-use" all your favorite views, both standard views and custom saved searches, both at work and at home and in whatever other types of "roles" you have defined for your life.