If you don't want to save the 'Check for'-expression as value for a slot you can use the JSON Editor. Thats important because otherwise we weren't be able to reformat a date or time before saving it. Saving multiple values of a pattern based entity is another example where we need this (see https://developer.ibm.com/answers/questions/420306/how-to-store-literals-using/).
Unfortunately these edits are not reflected in the simple editor. Even worse: These edits are restored (without any warning or questioning) to it's defaults by just clicking in the 'Save it as' field (see warning at step 4 in https://console.bluemix.net/docs/services/assistant/dialog-slots.html#add-slots). You don't even habe to edit that field! Afterwards the assistant does not work as expected anymore.
This behavior of the editor is very annoying and we spend many hours to find out under which circumstances our edits in the JSON Editor were overridden. Restoring these complex value expressions can take even longer because there is no 'undo'-function so far.