• Aesthetics and functionality: You can replace a big, heavy, or ugly bottle with something more squeezable, something more beautiful, or just more functional.
• Frugality: When you have a standard bottle in your kitchen you can just buy bags of generic dish soap, or buy it in bulk.
• Water it down: Most dish soap is much too concentrated. In fact, it's so concentrated that it doesn't do a good job cleaning the dishes. This is counter-intuitive but true; it takes a lot more water to lather it up and wash the slick, heavy soap off the dishes. I dilute my dish soap with an equal amount of water, and it actually works better (and lasts twice as long too).
These recycled soda bottles are a very cute option, especially for a bright mod or vintage kitchen.
You can do the same with vinegar or oil, too. I buy my basic olive oil in huge cans and refill a darkly-tinted bottle every week. The dark tint protects the oil from the light, and I have an inexpensive plastic pourer that pours smoothly.
What about you? Do you switch out your dish soap, vinegar, oil, and other kitchen liquids into a reusable bottle? Here are some photos from how other readers have done this.