.bss consumes "memory", but not a space inside the executable. Its sole purpose is to store zero initialized data (as you know).
.data (and related sections such as rodata) do occupy the space inside the executable and usually contain strings, integers, and possibly even whole objects.
A typical program has a lot of zero initialized data, so a significant advantage is that this data does not consume unnecessary space in the output file.
Regarding several sections *. data .... rodata / .data can be used as a hint to protect memory (prohibit overwriting .rodata, allow reading / writing to .data).