The usage of 'limiting composition'
These are called non-stoichiometric compounds or berthollides. Because the ratio of the fractional component is not fixed, but can vary over a small but continuous range, it would be pointless to try to express the formula as least common multiples (LCM).

For example, iron(II) sulfide can have a ratio from about $\ce{Fe_{$0.8$}S}$ to $\ce{FeS}$. So in LCM terms, the formula varies continually from $\ce{Fe4S5}$ through $\ce{FeS}$, including $\ce{Fe9S10}$, $\ce{Fe19S20}$ and so forth, all with similar physical and chemical properties.