I strip out a lot from system app so I get Redux to be installed at 75MB. Roms install on the /system partition. So with custom partition layout I can reduce the system partition to 75MB. On standard layout, system is 250MB. So I have saved 175MB, which has been added to the /data partition ("internal storage").
Also, since I no longer need much of a /cache partition, I have reduced this to 3MB, which means my "internal Storage" (or /data partition) is 360MB instead of the original 147MB.
It means I no longer need a partitioned SD card. Everything works on the internal memory, even with over 100 applications (like I have)