If I flash my ROM with an unlocked bootloader, will I lose all of my data?

[m_tte63]

Flash ROM with unlocked bootloader

Hi everyone,

If I flash a ROM (I would flash the M preview on a Nexus 5 with 5.1.1 installed) and I have the bootloader unlocked, will I lost all data using the ./flash-all.sh script?

Thanks in advance. :3