Slicing for html in picture or in layers

[photoshop16]

Hi,
I usually make a photoshop file and slice it partly into the picture itself (without layering everything) and party make layer based slices. It has been working well but now I have a coder who wants everything (all buttons etc) into layers, is this necessary or is he just being precise?

 

[gourhou]

Some one else ? i'm intterested to !