There are many technical answers on this forum, but what I usually explain to anyone who is new to astrology on this topic is – think of Over the Counter medicines, General Physician and a Specialist.
The Sun Sign predictions are at a broader level and have the capacity to help you in general terms. This can be compared to over the counter medicines which by your own know how, or some one else’s suggestions are safe to take. Taking a Crocin once in a while never hurts anyone.
Then come illnesses which involve some level of complexity and need a physician’s help. This is your Moon sign and will require an astrologer to be consulted. They do help you in some specific matters of life and also have some general usage in overall life matters. Also akin to prescribing low level antibiotics.
Now let’s get down to specific problem areas which are very specific in nature to a person and have a very personal connection to our lives. Things like my marriage, my job, my money which involve complexity which need some level of specialization. This is done by a astute astrologer using your Lagna or Ascendant, because Your Lagna is You. This is synonymous to getting into complex antibiotics while using other treatments to solve a complicated interdependent set of health conditions.
I feel there are two more levels of complexity which have to be considered – using Nakshatra and Divisional Charts. These can be considered as getting operated by a Neurosurgeon.
