If I install a custom launcher eg Nova on Stock Android 4.4.3, what inherently changes ?
Similarly if I were to then install a custom rom eg Paranoid Android, are the benefits gained from installing it then overshadowed or "lost" if I were to then install Nova launcher ?
To clarify wouldn't the experience of Stock Android with Nova and Paranoid Android with Nova be very similar if not identical ?
If you install a alternate launcher, the first thing you'll see is a difference in how the home screen, widgets, (maybe lockscreen if it has support for that), and the app drawer appears and works.
AFAIK that's the only changes you'll see from changing the launcher regardless of what ROM you use.
But one thing's for sure - depending on which ROM you get, the experience will change very little or a lot.
Each launcher has its own default appearance which will vary. Unless you tell the third party launcher to import you stock launcher settings and icons it will not have any customizations and you will need to set up the screens yourself.
The look and feel of each launcher will vary greatly. I use Nova Launcher on my S4 since I despise the stock Samsung Launcher. The screen transitions, default layout, and many other options are customizable with a 3rd party launcher that you don't get with stock. So, the experience can vary greatly depending on the settings you change in the chosen launcher. Nova has many settings I didn't bother to change but the ones I did change make a huge difference in the interface and experience from the Samsung TouchWiz Launcher.
You should not lose any benefits of a ROM by using a 3rd party launcher but you may not need the third party launcher depending on the ROM.
One feature of many 3rd party launchers is the ability to backup and restore your home screens. For this reason alone they are worth it. Particularly if you like to flash roms frequently. It can save a significant amount of time and agony if you don't have to reset all your home screens after each flash.
