Why would u wanna be able to do more chinups? You going into a chinup competition.
I remember Wendler saying he didn't want anyone in his gym who couldn't do at least 12 BW pullups.
the pullup/chinup is one of the most commonly understood designators of strength conditioning. Having a minimum number is very common on many fitness test for military/professionals.
Also its probably one of the best exercises for your lats/biceps/traps. This chain of muscles is used in almost any athletic endeavor to perform compound movements. If you can do a lot of pullups/chins you have a well conditioned pulling ability. Now as to whether your goal is to do more BW reps or more additional weight (i.e. 1RM but with additional weight) is kind of a less important consideration, tho if you can do more BW reps you could probably do more additional weight on a 1RM. It's not a perfect relationship as you can train either specifically, but there is some correlation.