Never had that work out for me.

 

No

 

Copy paste?

 

How bout just don't format it and manually delete whatever shouldn't be there (android etc)

 

I flashed a modded stock, PAC rom, Cm11, and the PAC rom one more time. My internal files stayed intact.
As long as you don't wipe internal in TWRP, everything in there will remain.

 

It doesn't because plenty of people actually keep all their data (pics, vids, etc) on the internal and imagine it backing up all that every time you wanted to do a nandroid (for someone with a 128gb phone which is full it would be a long time). Also whenever you switched ROMs you would take new pictures and if you restore the old nandroid you lose them all. My guess

 

It probably won't. Officially you only need to wipe data, cache and dalvik for flashing a new ROM since the ROM should automatically wipe system when it's installing. I personally never wipe internal and never have issues.

 

Same here... Usually Titanium and copy/pasting specific files will keep it active... Imagine using a phone with no external storage available. OTG stick and PCs saved me back then.