I am not a fan of being “born on the cusp” if you have a birth time and you cast a Natal Chart your planets will always be in a particular sign. The planet may very may well be in 0 or 29 degrees of a particular sign however a planet will never be in two signs.
Naturally we always have to consider the entire chart when taking into account the personality or psychological structure of a person, but decans are a fun and informative place to start.
People have often said to me I do not seem like the typical Cancer. I have a strong Pluto in my Natal Chart and I was also born with the Sun in 15 degrees of Cancer making that the Pluto Decan of Cancer. This indicates that Pluto will very much color my personality traits. If I was born in the last 10 degrees of Cancer this would indicate my personality would possess a strong Neptunian element. Some of my favorite women in life have Natal Moon in Leo; I was born with my Moon in Aries however it is at 16 degrees this is governed by the Sun or Leo so we can naturally see why I gravitate or appreciate women with Moon in Leo; we likely have similar traits.
Deacans are dividend up by degrees: