I had to do some research to get the difference between canned beans (which I do not use) and dried beans, which I use a lot of. (I do however stock canned pork and beans as a back up, that is just common sense.)
The difference between a standard can of beans and a standard 500 gram bag of dry beans is a lot.
Standard can of beans = about 1.5 cups of drained cooked beans.
500 grams dry beans = about 8-9 cups of drained cooked beans. This can vary based on the type of beans.
Convenience is one factor in using them, and smaller amount is another. However, one does not need to cook a 500 gram bag of beans at one time, it can be reduced.
Time is the other factor, one has to plan when the beans will be needed as it does take time to cook dry beans.
Cost is another factor. (Red Kidney Beans is my example)
Standard can of beans = 119 Baht at Tesco (this will vary by brand). Yield is about 1.5 cups.
500 grams of dry beans = 43 Baht at Tesco, all day long. Local brand as well. Yield is 8-9 cups.
The prices and quantities show the difference and the savings to you.