Home Assistant Previous Reading

Does anybody know what the entity previous_reading is for when adding a switch to home assistant? It seems to be the previous power usage reading but I dont know why I would want to know that.

I see this field on multiple switches (not just Inovelli switches). I havent found any true documentation on exactly what this means, but this is my assumption:

You should see 3 different entities: Energy, Previous_reading, and interval. You can take energy - previous_reading to get the amount of energy used over interval seconds.

I havent had a need for this information in my setup though, so I havent done much to validate my hypothesis.