Should I leave ZRAM activated on a device with 512 MB RAM or not?
Leaving ZRAM on may actually be beneficial to your little S Plus if you leave it on, though your limited use cases (Phone and Camera only) may not see a huge benefit over not having it on. The cache exists to keep commonly used programs, files, and useful bits of data on the memory instead of stored in a page file - this can speed up your phone a little and increase the lifespan of the device.