An incident meter tells you how bright is the light falling on a scene, and records the range of brightnesses in the scene where they naturally fall on the scale of tonalities.

A spot meter allows you to read the range of brightnesses in a scene and determine how well (or how poorly) they fit within the dynamic range of the film being used.

Different animals for different purposes!

For example, you might read with an incident meter EV18 as the inherent brightness of the light falling upon the scene. But then when you use a spot meter and read the darkest part of that scene you read EV13 and the brightest part of the scene as EV21, and you know that your slide film can only record 6EV of range (range assumption for discussion purposes only) while the scene is 9EV wide, so you get to decide to sacrifice the shadow detail (by shooting at EV18) or to sacrifice the hightlight detail (by shooting at EV16)