All sorts of things: in reading the styles of different writers why one novel's plot works well while another doesn't what makes great character writing what makes poetry vivid and moving
in landscapes how the weather changes the look of my world; it never looks exactly the same twice
among people why they react to the same stimuli in different ways
in food what's the freshest, healthiest and yummiest
in live music is it in tune and in rhythm? is it my flavour?
in drawing if I shift this line half a millimetre that way, will it more closely resemble the subject? will it improve the expression?
when the optician shifts the lenses this way, do I see more clearly or less?
In fact, every facet of everything we do depends on making sensory and cognitive comparisons, whether we're aware of it or not.