I often wonder why players would be open to unsolicited advice or instruction on the golf course. I have seen it countless times where someone will offer swing or strategic strategic advice without being asked. For full disclosure, I was (emphasis on was) a player who spoke up from time to time without any considering I was over stepping the boundary of being a good partner. Now back to current day. I think that many players would benefit from some advice, however I do not think that it should come from anyone without agreement from both players.
I play golf with a regular group. We have a predetermined agreement to help each other if we see something out of the ordinary. We agreed to this because over the past 5 years, we came to understand the goods, bads and uglys about our game. Thus, we are a good sounding board for each other and are not afraid to speak up when needed.
Understanding our agreement, we still confirm about unsolicited advice when the situation is something new or steps outside the arcs of fire we had previously established.
Our agreement stops if there is someone outside our normal foursome. With a new player, giving unsolicited advice would not be conducive to a harmonious round. When a new factor (player) is added to the group, we automatically revert to golf etiquette where we keep our yap shut unless asked. This is highly unlikely that the new person would ask, so we just play our own game without any sidebars on advice.
The only unsolicited advice I can offer is to know your group and keep your thoughts to yourself.
I am a grateful golfer! See you on the links!