I use them for so much. Water from showers and faucets while it’s warming up, stuff for the compost pile, to cart my tools around with me as I go about my yard chores. I have one to mix whitewash and one for scrubbing the interior of the coop. As you said they stack up nice in a corner and don’t take much room.I don't live in town, but somehow, I managed to get about 4 or 5 Harbor Freight 5-gallon buckets this past year on their weekend sales. I only go into town maybe once a week. If I lived in town, I would probably go on each day of the bucket sale and pick up a free bucket with supplies I need. Unfortunately, my old Ford Explorer is only getting 13 mpg so it costs me about $8 round trip just to drive in town and back home. Not going to make a special trip in town to get a $5.00 bucket for free, if you know what I mean. That would not be frugal.
Those 5-gallon buckets are also used a lot in gardening. Lots of YouTube videos on making them into self-watering containers for your plants. Never tried it myself, but looks like a good idea.
I’m starting a small hydroponic garden now so they’re good for that and I do want to try a wicking bucket or two so that’s on my list. I’ve read that hydroponics uses less water than traditional gardens and since our water is a huge concern I’m going to try it. Maybe pass the skill to the teenager who wants to learn and digs science.