A delivery order ensures you have full ownership of your cask. A delivery order is not the only way to transfer ownership but they are the industry standard way of transferring cask ownership at the warehouse level and so if you are not being offered one you should ask why.
If you do not receive a delivery order and you haven’t had confirmation from the warehouse where the cask is stored that the cask belongs to you, then it is highly likely that you do not own that cask. Therefore you do not have full autonomy over your investment.
Think of delivery orders as the equivalent of receiving the v5 document when you buy a car.
Remember: A certificate of title, acquisition, or ownership is not a substitute for a delivery order.
Further reading:
Do You Really Own Your Cask of Whisky?
“Personal Investment in A Scotch Whisky Cask” Summary of SWA Guidance