Don’t skip this step

Having the dog sit on an elevated surface helps to teach them to stay when told to sit or down and then you walk away. As the dog develops the self control to do this you can then ask for the behavior without the elevated surface. This just makes it easier for the dog to transition to a higher level of obedience.
For example, in settings where distractions are very challenging for a dog, having an elevated spot to stay can make the difference between the dog being impolite or polite during introductions. Eventually we want to work toward polite introductions where the dog is completely free and not confined to a specific spot, but jumping to this stage of obedience without place training can be asking too much for a dog who lacks the self control and understanding.