The differences between oil bars and oil pastels

This completely confused me when i first started working in oils.  Why the two different types of bars?  How to use them effectively? Why use them at all?

 To start with the differences:

Oil Bars are basically oil paint in a stick form.  They are thixatropic (forgive the long word but i love it and it took me ages to understand the meaning!) meaning sometimes fluid and sometimes gel - the neat oil paint stick becomes more fluid in use as it warms and returns to a firm gel state when allowed to stand.

Oil Pastels have a soft creamy quality with all the intensity and vibrancy of conventional oil colours.
Developed in 1949 for Picasso who was looking for a intense colour that could be applied directly and freely to a wide variety of surfaces.The Oil Pastels are made using a unique combination of oils and waxes. 

Using them effectively:
Because with oil bars you are using oil paint in a stick form, the drying time will be similar to the oil paint you are using in a more traditional format.  This makes it possible to use the same rules as you would for oil paint i.e. thick over lean layers.  Useful when you want to use an oilbar for underdrawing of your compositions and great if you want to mark-make on top of your established oil painting. Oilbars are best used on primed canvas or linen or primed paper.

Oil pastels have a creamy sticky quality because of their combination of oils and waxes and can be used on almost any surface, including paper without cracking or effecting the substrate.  They dry slowly - more slowly than normal oils and there is a fixative spray.  I find them immensely useful for sketching in 'plein air' and like to use the transparent  oil pastel as a mark-maker without adding extra colour.

Turpentine or the eco-friendly alternatives such as Zest-It will  blend both your oilbars or oil pastels.

Why use them at all:

It is the control you have using both oilbars and oil pastels that i find most useful. It would be great to hear your opinions on the pro's and cons?