The definitions are somewhat general and the lines between different levels of sedation/anesthesia can be hard to find. Also, given that different people respond differently to medications, the goal level of sedation may be hard to reach or it may be easily passed. Then, one has to be able to adequately care for a patient that is sedated beyond what was anticipated.
The american society of anesthesiologists recommends that if a provider intends to provide a certain level of sedation/anesthesia, then they should be trained, prepared and equipped to rescue the patient from the next deepest level of sedation, up to and including providing general anesthesia
with airway control and artificial ventilation.