The first application of custom searches is the definition of keyboard shortcuts for frequently used searches, either creating an agenda buffer, or a sparse tree (the latter covering of course only the current buffer).
Custom commands are configured in the variable
org-agenda-custom-commands. You can customize this variable, for
example by pressing C from the agenda dispatcher (see Agenda Dispatcher). You can also directly set it with Emacs Lisp in
the Emacs init file. The following example contains all valid agenda
(setq org-agenda-custom-commands '(("w" todo "WAITING") ("u" tags "+boss-urgent") ("v" tags-todo "+boss-urgent")))
The initial string in each entry defines the keys you have to press after the dispatcher command in order to access the command. Usually this is just a single character. The second parameter is the search type, followed by the string or regular expression to be used for the matching. The example above will therefore define:
as a global search for TODO entries with ‘WAITING’ as the TODO keyword.
as a global tags search for headlines tagged ‘boss’ but not ‘urgent’.
The same search, but limiting it to headlines that are also TODO items.