I think it depend on what has been grown in it and what you intend to grow, some diseases stay in the soil but saying that I often just rermove the top layer in my big pots

If you're sure there were no fungal diseases or things like vine weevil infestation in the old compost, you can reuse it. Some people mix it with new compost, others just turn it all over to break it up before replanting, but either way, you will need to add some fertilizer, since any nutrients it once had will be long gone. Growmore will do. Otherwise, spread it over the beds and borders in the garden.