I consider Lots one of the most important factors in astrological delineation, regardless of the type of astrological investigation being made. In this I am close to the Hellenists and the early-to-mid Islamic transitional era authors. The condition of the Lot (sign placement, house placement), the condition/relationships of its planetary significator (dispositor of the sign the Lot is in), aspects to the Lot (note: Lots do NOT make aspects-aspects are made TO Lots), connection of Lot (and/or its significator planet) with fixed stars, aspect (if any) of the ascending degree (or sign if using aspect-by-sign) to the Lot, the dodekatemorion ramification of the Lot (and any connection the dodek of the Lot has with stars, planets), midpoint of the Lot and its significator planet and/or the ascending degree, and so on, allow a great deal of investigation to be made regarding the subject matter of the Lot.
Most important single Lot (in my opinion) is the Part of Fortune; close to it is the Lot of Spirit (shows the inner nature of whatever it is you are investigating) But Lots can be used for many specific matters/subjects of astrological investigation.
To better understand the "philosophy" behind Lots (which go back to the early days of Hellenistic astrology in point of origin), the Zoller "Arabic Parts" books will provide a good foundation.