Okay so typically people will try to point out whoever is winning at any point at in time because it is very easy for people to snowball games and then attempt to get everyone to do their part to stop them. Particularly important when there is an important enchantment and people are playing grixis and you are the only one that can deal with it. There is almost always a point in my games where people ask everyone else if they have an answer, or wrath or a way to stop someone from winning.
There is obviously limits to this, a semi, fleeting co-op, it should always be a suggestion and never a command, do your own thing only help if it helps you win.
In my opinion, games are just better if everyone has built their decks with sufficient interaction that unless people are super unlucky one of you will have an answer card when a player plays a threat. so you shouldn't just sit in your corner and try to combo out faster than your opponents because everyone is going to get bored real quick.