Crontab defaults are non-intuitive

[kpsherva]

When scheduling a job to run with cron, fields are filled automatically with * which is dangerous behaviour, especially in case of the minute field.
If someone does not fill minute field, it is automatically filled with * which causes potentially expensive tasks to run every minute without the administrator ever realising (before it is too late).
The schedule UI should either be explained well, or provide less invasive default values (or validation).