Somebody on my Orkut Vedic Astrology Forum asked me the difference between Lagna Chart (Rasi Kundli) and Chalit Chart. I believe that it is very important and least understood point in Vedic Astrology. In my recent post "Tips to the Astrologers", I hinted the answer of this question but there was no elaboration. Here is a little detailed reply.
The Lagna Chart, also known as Rasi Chart, talks about the relative positions of planet for identifying the nature of the planet (benefic/ malefic etc.) and relationship with other planets. For example, a planet 6th, 8th, or 12th from lagna is not good for langa. On the other hand, Chalit chart tells about planet's house position also called planet siginifcation. For example if a planet is in 8th in lagna kundli but in 7th in chalit kundli, it means that you will get the result of 7th house during the dasa period of that planet. Due to being in 8th in lagna chart, the result may be malefic, so it shows problem in marriage.
Assessing house position from Lagna Kundli is not correct. This is the reason we see cuspal chart is being used in KP System for assessing the signification and synthesizing the result with dasa. In case the planets are shifting in Chalit Chart, in dasa period of a planet, it is recommended to predict the result of house with which the planet is associated in Chalit chart and NOT in Lagna chart.
The Chalit chart requires some mathematical calculation and that is the reason it was not very popular. But now with easy availability of computers, it is important that astrologers start using Chalit chart.