The mix of oils you use will affect the qualities of the lather in your finished soap as well as how quickly it solubizes in water. If you play around in soapcalc.net for awhile you can see what each oil brings to the table with respect to bubbly lather, creamy lather, conditioning, cleansing, etc.
Classic Castille soap is 100% olive oil, water, lye and nothing else. It takes a long time to cure and makes a nice gentle soap. Some soapers make 100% coconut oil soap (with a steep lye discount so it's not too drying). It's all a matter of what qualities you're looking for.