First, what is the difference between Any Form Post and Current Page Submit? 
Any form post means that any form from any website pointed at your page will trigger it, please never ever use this. Current Page submit is more secure as it checks that it is your page that is submitting the data (although this can still be spoofed)
And second, what are some practical applications for using a dynamic trigger, such as a recordset value or session variable? How do those work and what are some practical uses? I feel that I'm missing something I could be using and instead I'm creating more work for myself when I don't need to be. 
If you want a particular update or insert to happen only if a certain piece of data is present then that is what you would use these for.


