From the artist's point of view working with dry traditional pastel is closer to drawing than to painting. One builds up form through touches or line. The colour doesn't "bleed" into the ground and unlike water-colour it stays constant since it doesn't need to dry.
The technical disadvantage is, of course, the fragility of the finished painting . Even when fixed they are susceptible to rubbing, so need to be protected in frames behind glass, and they'll fade if exposed constantly to strong light. I use pastel at times of the year when nature evolves rapidly; during the springtime or autumn for example. Small pastels are usually finished after two or three days work, with each session lasting a couple of hours while the light remains constant. Like this I can work on three pastels a day which gives rise to "series" of related work.
I pastel in places where oils would be inappropriate: in a boat, for instance or standing on the ledge of a cliff. I used them exclusively when working in the central Indian city of Bhopal among dense crowds of onlookers. They have a directness that other mediums lack. You don't need a brush or a knife, it's like having coloured fingers! Here is a selection of my pastels (without individual commentaries).