indeed... you can set the system wide default format for a timestamp to be that.. but bear in mind then that oracle will only thus go and do an implicit TO_CHAR or TO_TIMESTAMP using that format string..

In all programming situations, it pays to be explicit rather than implicit; assuming a computer can think gets you into trouble.

additionally, when deviating from the default values, you should be aware that your change may break other code that also does its work implicitly with the old format. If you ahve a legacy app that is inserting or selecting timestamp data and is expecting it to be in some particular format, you potentially just broke it

The solution? Dont change defaults. Dont rely on implicit conversions. Be thorough now to avoid debugging later