I think it is in the area where Paul said that everything is lawful for him, but he will not allow himself to be under the power of any. There are many things in the Mosaic Law that are not exactly part of the moral law. This means that as a converted believer I need to abide by God's moral law to the best of my ability and use 1 John 1:9 when I fail.
But there are many other aspects of the Mosaic Law which were binding for the Jews, but not binding for New Covenant believers. Although Paul is bound by the moral law concerning adultery, fornication, lying, stealing, hatred, murder, rape, etc which he identifies in Galatians 5 as the works of the flesh, he is not bound by the food, ceremonial, food offered to idols, tattoos, wearing of jewellery, etc., which are amoral - but he says that if a believer engages in something that upsets his conscience and is sin for him, it is better to avoid it so that he keeps his peace and not allow his faith to be upset by any condemnation bombs from the devil.
So when Paul says that all things are lawful for him, he is talking about the amoral requirements of the Mosaic Law. But he is aware that "weaker" believers may have scruples about certain things, like jewellery and tattoos and eating certain foods associated with pagan worship, so that although Paul would not worry at all about doing those things, he is aware that in the presence of a weaker brother or sister, he needs to abstain because he could influence that weaker person to copy him and therefore do something that might wound that person's conscience because although it would not be sin for Paul, in the mind of the other person it could be sin. Therefore Paul would not want to do anything that would compromise another person's faith in Christ.
In actual fact, smoking and drinking alcohol are in the same category. Some do not see doing those things is sin for them, but for others they are sin, therefore, to follow Paul's advice, it is better for a smoker or drinker to refrain in the presence of a believer with a weaker conscience. This is part of loving our brethren in Christ and not causing offence.