On creating all the activities except Custom activity, if scheduling of any activity conflicts with the same activity it shows alerts only if enabled from the backend configurations.
On clicking Ignore and Save button, activity gets saved but with conflicting error message on the activity. Clicking Cancel button, scheduling gets cancelled and you again get to re-schedule date and time of the activity.
Note: You get scheduling alerts for all the activities except Custom activity. And it works only if conflict management is enabled from configuration page.