When you design a call tree so that any data used later is passed explicitly down the call tree instead of looked up by ID over and over, then you can be sure that all of the decisions about that data are made on a consistent copy of the data.
When you look up the same value 10 times, you not only pollute the flame graphs and call counts which makes proving that a better algorithm is necessary or has any effect much harder, but more importantly, you could get 3 different states and try to make a bunch of updates based on what should be mutually exclusive states in the system. That's the global shared state problem.
When you look up a value once and remember it throughout a calculation, it may not be the current state, but at least you have a clean snapshot of the data. Which in situations such as cancelling an account immediately after getting one last discount on a purchase, well, we know which scenario the customer probably meant.
