I agree with the others, but want to add that linear animation is useful and important for some types of movement. For example, if you cut from one shot into another, and in the second shot, objects are
already in motion, then linear keyframes are suitable. If you cut to a camera that's panning, or whip-panning, for instance, it will start with linear rotation. If you cut to a record player that's already playing, it will have a linear keyframe at the beginning. If the same record stops playing, it will decelerate gradually, and use a curve (ease).
Another example of where you'd use linear is for something that's flying into frame. Say you've got a title that you want to come on screen quickly. It could start from just off screen (top, bottom, left, even "over the shoulder") with a linear keyframe, and land with some sort of gradual deceleration -- smooth, sudden, springy, bouncy -- it's up to you.
If you start throwing the same kind of easing on everything, your animations quickly become mundane. Just like with good writing, it's important to mix up the structure of your motion to keep people engaged. There are several typical ways in which objects accelerate or decelerate. This page is a good reference for many of them. It includes graphs, video examples, and code snippets:
http://www.motionscript.com/articles/bounce-and-overshoot.html. Resolve doesn't really do these kinds of curves unless you jump into Fusion, but Fusion is very capable.