Locking is a hugely important feature. As you might know from cloud file sharing, the option to save changes to multiple copies of the "same" document is a disaster, often forcing someone to choose the "real" one to keep and losing data from the others.,
Big Business locks records whenever there might be a conflict:
someone else is changing the record? it is locked so you cannot make changes
another transaction applies to the record? you cannot change a paid invoice
another transaction relates to the record? you cannot pay a changing invoice
As you know from shopping, when you return something you purchased, they might cross out on your receipt but in their own record keeping they create a new entry, a negative qty return, with a negative payment refunded to you, which is perfectly clear.