Generally, if you have too many points in a model you risk getting oscillations on the path since you have a hard time putting the points into the exact location where you need it. So having more points than strictly necessary is sometimes a source of error.
Second the location of the anchor points matter for humans, So humans tend to want to have minima and maxima of the curves split if possible. This makes it easier to modify the design later. Also if you make fonts you need to have minima and maxima and animation is easier.
The third is that you want two adjoining shapes to share the points or you may experience tearing.
The above reasons are quite big and go to the heart of how to use bezier (and b-spline) paths effectively. But there are others.
Fourth reason is manufacturing related, so eventually you end up wanting to cut out designs that are not square. Now if your curve has a lot of control points then the CNC cutter needs to slow down to each span as to make the kind of continuity you intended. This can significantly slow your job down. Now you may be wondering what does it matter, but i have seen works that could easily have had less spans be cut and the cutting time was 30 times longer than the proper curve with no noticeable difference in result. You dont want to pay 30 times more for the job for the fun of it?
Fifth indeed less points is a smaller file, though not necessarily more preformant.