Generally, I tell people, the size of your crystal doesn't matter. In theory, this is correct. In practice, however, it really isn't quite true.
Smaller crystals work great for smaller situations
For instance, smaller crystals used in jewelry are fine. Mostly, you're interested in the stone's energies affecting your personal space so the amount of energy emitted by smaller stones is fine. Crystals put into your drinking water, those used for gardens, dreaming, office work, energizing food, and other such tasks don't need to be very large. However, if you want a crystal that can impact a large area, you might want to invest in a larger stone.
145 pound single self-healed point
In 1986 there was a store in Olympia, Washington, called Earth Magic and I used to go there regularly. The store focused on crystals and stones. The store is still there with new owners and is a more general metaphysical store. In 1986, Earth Magic was the only local store I knew of that had large stones, stones that weighed over 100 pounds. At any given time, they might have seven or eight of these giants in the store and I would go visit them when I could. One day, I fell in love with one of them. Not only did it have an almost perfect point, but it sported rainbows and it was self-healed. It weighed 145 pounds. Alas, what to do? Buying one of these just wasn't in my budget.
The stone communicated that it was a community stone and wanted to be with me in my business. At the time I published a newspaper called The New Times and served the metaphysical community. I told the stone about the little issue of my needing money in order to adopt the stone. If she wanted to move in with me, she had to help manifest the finances to do it.
Meditating for a solution
I sat in meditation with her for a few minutes and was inspired to ask the store owner if she would let me put the stone on lay-away and pay it off over a few months. She was delighted to do that and immediately put a "sold" sign on the crystal. I gave her a down payment and then gave her monthly payments until the crystal was paid off. Just the other day I found a letter she had sent me as the receipt and proof of our agreement!
A community stone
This large stone has been with me ever since and in this case size matters. Although I did take her to a large community event one time, mostly she has been an anchor stone for community energy. When I used to have a public office, groups would meditate with the stone and more than one person has lain on the floor letting their crown chakra touch the stone while they meditated. Her healing energy is palpable. I was also told that she has a twin. Two of them were rescued from the same mine in Arkansas at the same time. The other one is at a Ghandi memorial somewhere, but I haven't been able to find out where. Here's a photo of my crystal.
Where are the other large stones?
Frequently, I have wondered where the other large stones have gone. Are they in massage rooms, private homes, or healing offices? There aren't many of these larger crystals around, I have been told, because many of them were broken up to be used in computers and other electronic devices. My heart hurts when I think of those beauties being destroyed.
In most cases, size doesn't matter
In general, the size of a crystal doesn't really matter because most of us use them in our personal or healing spaces. What's more important is how you resonate with the stone and use it with intention and respect.