The advantages are that it will be easier to build apps this way because no outside server is needed. This is great for prototyping and bootstrapping. Apps built on Bitcoin have other advantages like maintaining data provenance (useful for audit purposes), managing data ownership (who is allowed to update a piece of data), or storing cryptocurrency atomically with data.
Frameworks along these lines are starting to pop up. One example is the Bitcoin Computer (http://bitcoincomputer.io/): It allows you to write an app entirely as frontend code and gives you simple provisions for persisting data on chain with a single line of JS code.