First of all I'd like to thank Latha from Zoho Creator support for the detailed answer and sample application.
"Zoho Creator can perform the functions you mentioned in your blog like Hide/show field values based on values in other fields, change the value of a field based on value selected in another field, validate field values, make read only values etc. by adding Deluge Script."
I'd like to make several examples of how Deluge Script looks implementing all above mentioned actions.
Сustom validation of form data:
Modify form contents dynamically, on form load:
Perform an action after a form data is persisted (for example, send email notification):
Perform field actions (like show/hide fields based on value selected in another field):
Display items in a dropdown based on selection made in another dropdown:
Well, Zoho Creator makes forms really dynamic and the flexibility you get can surpass other systems, but just in case you are capable of Deluge Scripting. I think, the main peculiarity (or problem?) of Zoho Creator is the fact the user can't do a thing without Deluge Script. Of course, you can do a lot of stuff with it, but unfortunately there is no golden mean option.