To be more clear: if a 16-bit instruction is 32-bit aligned, then you might want a 16-bit noop so that the instruction following the noop is also 32-bit aligned. But, in that case, you could just use a 32-bit aligned 32-bit instruction at the same location. No padding, one instruction saved, and the following instruction is still 32-bit aligned.

If the 16-bit instruction isn't 32-bit aligned, then the following instruction will be 32-bit aligned with no padding.

So, the question is equivalently: "Why would you ever want to add padding after a 16-bit instruction in order to force the next instruction to not be 32-bit aligned?"