I can give a kind of general answer.
The ActionSetfield widget may be used by way of a hack to create new tiddlers silently in the background, since setting the value of a field of a non-existent tiddler currently results in the missing tiddler being created quietly in the background. However, this did not fit all of my requirements, hence the ActionMaketid widget -- some quick notes:
-- There is no option to open the list of new tiddlers in the story river nor open the list of tiddlers for editing (or indeed, with two ActionMaketid widgets, some mix of the three scenarios).
-- The ActionMaketid widget came derived from a line of widgets whose purpose was the creation of multipurpose buttons
-- The ActionMaketid widget requires a list of titles as input (and can create simple series of tiddlers, such as indexed with an integer on its own)
-- I cut down one of Tobias widgets to be used for more complex cases
-- There may be cases where the ActionSetfield method is either sufficient or superior to the MakeTid method
-- I began be using the ActionSetfield (actually my old SetField widget) method to create tiddlers by default and wrote the ActionMaketid to do some things impossible with the ActionSetfield method
-- nowadays I tend to try the ActionMaketid first (its made for the purpose)
regards