There are two great basic reasons to be filled with the Spirit of the Lord. One is to have more access to Who He is. Another is to give Him more access to who you are.
Once isn’t all there is, either. Be refilled at every opportunity. There are rooms in the dwelling place you call your heart that He has not been given the keys to, and they are locked. He wants to be there as much as He wants to sit in the formal living room, where all the furniture is covered with plastic and the big fat family Bible sits on the coffee table.
He isn’t afraid of any of the rooms in our hearts, and we shouldn’t be afraid of His presence bringing light into the darkest corners of any of them. He wants the place to be full of Life and Light and Love.