If you let your end-users build their own forms. We once wrote a workflow definition and runtime engine at nestyle.ch using Magritte, where the users could build their own forms and define validation conditions on the form elements, all from the web- browser without programming knowledge. The meta-model is then stored in OmniBase. That's way I payed so much attention to make everything serialize-able. That being possible is one of the key advantages of Magritte over other meta frameworks, e.g., Mewa expects a lot of blocks everywhere.