Have you noticed how no one wants to be told they can't do something? The attitude is "I can do whatever I want". If you try to tell someone that limits exist the attitude you get is "Who are you to tell me I can't do something?" We believe we have an inherent right to do whatever we feel like doing. This might be true if we were the last person on earth and there was no sovereign God over all but because neither of these are true, Paul has a response to this attitude:
"... not everything is beneficial."
"... but I will not be mastered by anything."
I guess the Corinthians were trying to make a point about grace; that God's grace covers everything. Paul's point is that even if God covers everything there is no benefit to sin. What good ever comes out of the things we have been instructed not to do? Have you ever benefitted from stealing where your conscience has not weighed you down? Have you ever yelled at someone where it still felt good 3 days later? Was it beneficial? We may be able to get away with things because of God's grace but there are natural consequences to the things we do as well.
We also not alone in our life. What may seem to be good for you may have terrible consequences on someone else. Having sex with a girlfriend may seem good in the moment but how is she going to feel the next day? How is your future spouse going to feel about that moment? What will the benefit of tbis 15 minute pleasure going to be in ten years?
Sometimes these things we feel we can do in grace can also lead to our slavery again. There is nothing specifically that says I shouldn't drink, take drugs or gamble but these are all powerful tools of enslavement. They are things that we hand our authority over to so that we soon are mastered by them. Don't believe me? Well let's talk in 10 years. We can be mastered by any sin when we give it authority. Things like lying, sex, work, shopping, gossiping all can take mastery over us.
We were created to be mastered only by God; we belong to him, bought at a great price. Why would we want anything else to have mastery over us? Where is the benefit? The only benefit that exists is that which we find in our relationship with Jesus. Everything else is a short term contract that ends with the grave. We need to be very careful here to make sure we do not slip into this attitude. We only want to do this that bring honour and glory to God. That thought should guide us in all we do and say; to God be the glory.