Should the Ascendant start from the middle of the 1st house?

[astro_abc]

Hello All,

My astro software has the option of starting the Ascendant from the middle of the first house (this is the default setting) but it also has the option of starting the Ascendant from the starting of the 1st house?

With each settings, a few planets in my horoscope change houses.

1) What is the use of these two different techniques? Which one should be used?

2) Is starting the ASC from the start of 1st house called the Chalit chart?

3) There are other house settings - Parashari Houses or each house is 30 degrees. What should be used?

Thanks!