BLOCK_SIZE?

Little question that I already posted here a week ago or so. What drawbacks can suffer if one changes BLOCK_SIZE in include/linux/lvm.h from 1024 (or 4096 on S/390) to 512? I can't understand from code what't a real purpose of this constant, -- lvm seemed to work well with BLOCK_SIZE=512, no troubles so far, -- but i'm still not shure if it is "legal" to change that. At least there is some purpose on having different values for this constant on S/390 and other platforms, -- again, can't see that purposes...

Oh yes, this is about 2.2 kernel and lvm-0.9.

Thank you.

Regards,
Michael.