If you overwrite a ROM with a different one (different android version, or by a different developer) you may run into issues where it will not boot, or it may run poorly, random reboots, sleep o death.
When changing ROMs it is HIGHLY recommended to wipe the system, caches and the data partition (wiping data is not the same as FORMAT DATA in TWRP). There are some system settings stored in the /data/ partition that may conflict with different ROMs.
Most of TimDuru's KatKiss ROMs you can forward flash (even to new versions of Android) but you CANNOT go backwards. I flashed from 4.2.2 to 4.3 without wiping data and had no issues. However, if you tried to flash from 4.3 to 4.2.2 without wiping data, it will not boot until you wipe the data partition.
I have not tried this with the 4.4 version of his ROM (I am still on 4.3 for now.)
Oh, and yes, the addiction is called CrackFlashing.
Always ALWAYS make a backup in TWRP before flashing a new ROM or even an upgrade to the current ROM. If you want to go back to 4.3, make a backup and then use Titanium Backup Pro version to extract any apps and data from the 4.4 version and restore to 4.3. Do not restore any system settings or apps.