There have been some places in which a conceptual difference (that of criteria of identification, etc) is avoided in the categorical notation, namely

Let $Cat$ be at the same time the 2-category of small categories and its subjacent 1-category i.e. the category of small categories (...)

Why one can do this? The 2-category CAT and the 1-category Cat are not remarkably different? What is Cat (generally) in the literature..?