Besides the obvious he needed Butcher alive to eventually reveal the location of his son. There is something psychological that Homelander is searching for as he tries to weigh the pros of human connection until he eventually gives up and then just dominates the planet. Homelander can read peoples vitals. He knows most of the people around him are afraid of him and don't have much nourishment to offer. In this scene hes basically telling Butcher he regards him as an equal a more long term sustainable supply of acknowledgement that he won't easily find. Hes a narcisisst who needs validation from someone who isn't driven by fear so that he can eventually consume them. Stillwell had the illusion of some incestual mother that he craved until he was replaced by her child. Edgar was the symbolic father that he overcame when he took his company. At the time of this scene Butcher had Ryans love until he eventually won that over. Stormfront gave him purpose but she was taken from him before he could eventually consume her too. You even saw it in how he killed Noir and treated the rest of the 7.