Suppose we have the following chemical formula, say ammonium dihydrogenphosphate (NH_4)(H_2PO_4). This is the ammonium salt of phosphoric acid, H_3PO_4. Its elemental composition is NH_6PO_4, and here I have simply added the elements; but such a composition makes little chemical sense in that it is not immediately obvious that it is the ammonium salt of phosphoric acid, as the first formulation does.
Alternatively, I could have a transition metal complex, say [Co(Me_2NCH_2CH_2NMe_2)_2Cl_2]Cl. If I made this and sent it off for combustion analysis I would present it as CoCl_3C_12H_32N_4. After combustion, the carbon would come off as CO_2, the hydrogens as H_2O, and the nitrogens as N_2, and I would get a very accurate determination of the purity of my compound. A Mohr tritration would give halogen content.
If this doesn't address your question, would you clarify?
