While I work in almost all mediums, I must admit soft pastels are my favorite. I started using them mainly for practical reasons. When my children were younger I often got pulled away from my painting time and unlike oils or acrylics, pastels don't dry up! They just lie there patiently until you can come back to them. In time, I learned to love this medium and it's ability to create brilliant color.
Some people are curious as to why pastel paintings are called "paintings" when pastels are actually a dry medium. I believe the reason for this is that the application of color is applied to the majority of the surface unlike a drawing. Pastel pigments are actually the purest and longest lasting of any medium.
I prefer to use the softest pastels on specially sanded papers or boards. This allows for pure color to be applied in many layers without the color becoming muddied.
Unlike oils applied on canvas, pastel paintings are somewhat more fragile. It is typical for an artist to "fix" the painting with a spray fixative to avoid the colors being rubbed off. It is never recommended that anyone but the artist "fix" the painting as colors may darken or change with improper application.
Pastel Paintings are typically matted and framed. The matting acts as a barrier to the glass actually touching the painting. Proper matting and framing ensure that a pastel painting will last as long if not longer than any other medium.