When words are many, sin is not absent,but he who holds his tongue is wise.Proverbs 10:19
The first time I read this I was deeply convicted by my "free speech". I used to speak just about everything that was on my mind. This often got me into a lot of trouble (as I'm sure anyone with chronic foot-in-mouth disease can attest.) As I grew in Christ I found myself saying less and less. One day, after being convicted of this yet again, I prayed, "Lord. Please afford me the wisdom to know when I should remain silent." The Lord did not respond... as if to say, "Follow this example."
But simply remaining silent does not ALWAYS benefit. Ephesians 4:29 says:
Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen.
...and just a few lines down in Proverbs we read:
The lips of the righteous know what is fitting,but the mouth of the wicked only what is perverse.Proverbs 10:32
This is more than tact. The righteous know that there are words, innuendos, and topics that are not appropriate, ever.
There is a story of a preacher who was visiting a family in the church he served. The father said, "I have a really great joke for you. I'll tell you as soon as the children leave the room." The preacher replied, "then maybe you should not tell it."
Brethren... "live by the Spirit, and you will not gratify the desires of the sinful nature." Galatians 5:16