Hi,

It sounds like we are talking about the validation > required choices here.

If Set to "No" there is no validation on the control and its not required and can be left empty at the time of submission.

If Set to "Yes" the control has to have contents in it before the form can be submitted or a validation error will occur.

If set to "Expression" this lets you put a condition in so that at certain times the control needs to have content but at other times it does not.  Example would be to add "Is New Mode" as the expression.  This would mean that the control requires contents when a new item is being submitted but if you edit the form afterward and clear the contents there will be no validation error.

I have attached an example form the shows the difference for the options.

This does not answer the question about Causes Validation. The example shows how to configure validation but what's the purpose of the Causes Validation selection on a button? You can change it to 'No' but that has no impact - when you click that button it still performs validation. 

If you have a long form that users want to fill out over time before submitting, you should be able to have a Save button that does not require validation, and a Save and Submit button that performs validation. Otherwise, users can't press either save button until all data is filled out. So, back to the original question - is there an explanation on the purpose of this specifice option in a button control?