Guerilla is a visual tag editor. Although it can visualize bitmaps and play sounds, it is primarily focused on editing and viewing the structured fields which comprise tags. It does not offer ingame previews or interactive placement of objects, which is Sapien's role.
It is rumored that Guerilla was created later in Halo's development and tags may have previously been edited using something like Tool, possibly leading to some of the invalid tag data seen in the game's maps.
Using File > Save/Load Workspace, you can save and reload a file which contains the current state of open tags and their window positions. Guerilla automatically creates a file
guerilla.cfg with the last window state when closed.