On a client's boat we visited recently, every connector on the batteries, distribution bars, and DC panel were the exact same ring hole size, despite being connected to 3 different size studs. It looked like whoever did the work simply went to the store, bought a big bag of the same connectors, and used them everywhere. This is the simple and cheap way to do it, not the correct way. Using the appropriate ring sizes will improve the electrical connection, and reduce the chances of the nuts coming loose.
To connect a DC system properly you need a huge inventory of connectors. With 7 different sizes of main DC wire (8awg to 4/0) and generally 3-5 different hole sizes of rings for each wire size, it adds up quickly. However, it is important to have an inventory that is big enough for a job. If someone is doing work on your DC system and doesn't have 100s of connectors with them; they are probably either going to be doing it wrong, or will be making many time consuming trips to the store during the job.