The 27+1 constellation can be seen in the zodiac family along the ecliptic. Ashwini to Rewati,each sign contain nine navmansha ,which are equivalent to nine plants. If lagna ,lagna lord ,moon or more then one planet reside in a particular planet,the ruling plant of this nakshtra will start playing an important role in the birth chart. So that is why i call it key nakshtra.
The ruling planet of key nakshtra posited in kenda ,trikona ,friendly sign ,own sign or exalted sign can give excellent result to the native.In my opinion all the nine planets are playing the role of energy changer .For example we switch on the bulb in a dark room, we can see the brighter side of the room .Its doesn’t mean darkness been banished or vice a versa no its still there only we change the energy.
Similarly when we see the person is going through a particular phase of the life as a astrologer we say this is time to grow or fall in your life.But if you consider we just talk about MD,AD or PD,what about the transit?Slow planets take a long span to shift there role but fast-planets interchange there energy in very short time periods.Indeed moon is fastest moving planet in among them all but if we ignore moon and its interchanging energy, ( though we can not,because its control our mind and emotions)so rest of the inner planets are playing major role in our daily life .