Every degree
Every degree is part of the zodiac measuring system. The zodia is a reference for our annual solar cycle/orbit and was originally used to mark the seasons and our progress through them. In a cyclic sense each degree is equally important, one step on a long 360 degree journey. The signs of the zodiac originally related to agricultural and seasonal meanings; the birthing of lambs (Aries), the gathering of the harvest (Virgo), the paying of taxes (Libra, sharing a portion of the harvest), etc. Signs were useful shortcuts or references. The practice of giving some degrees importance was/is related to the form of astrology being practiced and the era in which that system of practice was introduced. Certain Hoary practices have already been mentioned in this post. Another practice involves the importance given to certain fixed stars (Algol is terrible, Spica and others each have given attributes). Current astrologers debate the merits of one house system over another, while other astrologers ignore the whole issue by considering that a planet moves into the next house when it passes the cusp of the sign that rules that house (even though a "house" may not start for many degrees later). Then, there are the "symbolic" meanings of each degree (astrology's version of tarot meanings, perhaps). This can go one forever. Me, I just use the darn degrees for measuring positions and aspects, its so much easier that way. Dave.