Root M8 question

[the_rooter]

Hey guys I have a quick question. I am a long time user with android and rooting and flashing isnt anything new to me, but I have a question on something that is the first time to happen to me.

When I sometimes go and flash a rom it fails. I go and try to wipe dalvik and cache, and system and it says cant mount system. All in red letters in TWRP 2.8.0.3, I have to reformat to fix the issue.
First question: Is it bad to format everytime I flash? should I do it? I normally dont until I notice the error to mount system. It happened when i was going from sense based rom to aosp. I am on the updated 4.4.4. I asked this on xda with no answers. thanks

2nd question: does the error system mean that the internal card is dying?

 

[vosg]

It's possible that a ROM uses another partitioning than the one that you have installed. In such case, you should carefully read the ROM developer's instructions. Possibly you have to flash the .pit file as well (pit stands for partition information table).

 

[techsavvy01]

Yeah be careful buddy