of benefit
Giving or acting as a benefit (to someone or something); serving to help, promote, or enhance (someone or something). If you think this new tax law will be of benefit to anyone other than the top 1% of citizens. I've heard enough. There are too many unknowns and not enough of benefit in this proposal for me to accept it.
of benefit (to someone)
serving someone well; to the good of someone. I can't believe that this proposal is of benefit to anyone. Oh, I'm sure you'll find the new health plan to be of benefit.