I think it is as valid a source of information as most others. I would not call it accurate but it can give you some guidelines. If you are just dealing with Sun signs it is useful to know that each sign as an element and a quality assigned to it. 12 signs one of each combination. The qualities are Cardinal, Fixed and Mutable. The elements are Fire, Earth, Air and Water. In the case of Tauraus it is the Fixed Earth sign. Anyone ever call a Tauraus stubborn?
The Cardinal signs are: Aries, Cancer, Libra and Capricorn
The Fixed signs are: Tauraus, Leo, Scorpio and Aquarius
The Mutable signs are: Gemini, Virgo, Sagitarius and Pisces
The Fire signs are: Aries, Leo and Sagitarius
The Earth signs are: Tauraus, Virgo, and Capricorn
The Air signs are: Gemini, Libra and Aquarius
The Water sign are: Cancer, Scorpio and Pisces
Signs you share a quality with are more difficult to interact with than signs you share an element with. That is only generally speaking and I don’t put a whole lot of faith in it. I do see patterns in my own interactions, how much of that is self-fullfilling prophecy and how much is Astrology is subject to debate.
You can of course get deep into this with charts and houses and aspects of planets to one another and how they aspect to planets at birth. But I tend to stick to the above info as a “I can probably expect a (fill in sign) to be…”
This information is useful primarily for chatting up girls.