A spot meter is handy to be able to read the reflectivity of an object in the scene precisely from a distance.

It is like putting a telephoto lens on a meter to isolate one part of the subject.

An alternate method is to walk over to the subject and read the reflectivity close-up.

Without a spot meter, you would take a reading of the average light reflectivity of the whole scene. This would give you an average exposure which may or may not render an object in the scene to your desired liking.

You could take a reflection reading of a grey card which represents the mid-grey of an average scene. This too would give you an average exposure which may or may not render an object in the scene to your desired liking.

The spot meter allows you to more accurately measure an object in the scene easier than moving the meter to each object.

There are two kinds of light meters that read luminance either falling on the scene (incident) or being reflected from the scene (reflection). After that, there is the acceptance angle which determines their accuracy. How you use it is more important than its type.

Any meter will be a disappointment if used incorrectly.