Hi Mr. Cheok Yan Cheng

You're right about your code. you can use

mov sp,#any

It's correct but reserving is more than declarartion. it protect your memory location.
you can be sure that when you add another memory it won't be overlap with others.

For my experiences I use C and assembly together.In C there's no need to manage your physical memory directly
(compiler will handle it)
so reserving segment is needed in assembly .For protect using of these memory area.