Improving your chess can often be a frustrating business as progress seems almost non existent at times. You might easily be getting stronger but the incremental improvement (for example seeing things a nanosecond faster) might not be noticeable without an external source of measurement.
This is where ratings come in useful as they provide a reasonably accurate measure of playing strength over time. If someone shows a stable rating improvement (i.e. it goes up and then stays up) it means that their chess has improved. This can help considerably to ease any frustration.
Are there any negative sides to following chess ratings? Yes indeed there are and Natalia Pogonina wrote a good article about this here.
I’d like to add that considerable confusion is generated by the fact that the various rating systems across the World are not standardized which means that people can get the wrong picture of where they stand in the food chain. The accepted ‘norm’ are the ratings worked out by FIDE, but different nations have there own systems and then there are those estimated for you by computer programs and internet server ratings. The latter are probably the least accurate in general but it depends very much on which server is being used.
Accordingly I’d recommend just using these ratings to measure changes, going up 100 points is better than it being the other way around! There’s a case too for taking a long term view for example via a monthly ‘high watermark’; monitoring it on a daily basis will produce wild and meaningless fluctuations.