question about internal memory

[xFuse]

ok, so sadly last year when i knew nothing about android i bought an i9500 S4 and the internal storage always bothered me so i flashed many roms including cyanogen and my question is:
(just a heads up.. a total tech noob)

how come i never got any extra memory after flashing roms that weigh so much less than the stock touchwiz rom?

 

[Hadron]

The reason is that the internal storage is partitioned. Samsung allocate enough space in the /system partition for their ROM plus any bloatware that the carrier might wish to install. If you then install a smaller ROM that leaves free space in the /system partition, but as user-installed apps and data live in the /sdcard partition that doesn't actually give you any more space.

You could use Titanium Backup to move stuff to the /system partition, but beware that if you reflash the ROM anything you move there will be erased.

On some old phones we used to repartition the storage to free up space, but I don't know whether that is something people do with the S4. The best place to find out whether that's an option would be the appropriate "all things root" subforum of our Galaxy S4 forum. Of course if people have developed tools for that for the S4 you then need to make sure whatever partitions you use are compatible with the ROM you want to flash (on my old HTC Desire a partition scheme designed for CyanogenMod would definitely not work if you wanted to flash a HTC Sense ROM, for example).