LeBron is 3-5 in the NBA Finals, and with how dominant the warriors played combined with how weak the eastern conference is, he could very well end up 3-6, 3-7, or 3-8 which is pretty bad 
If LeBron goes to the Clippers, Lakers, or Spurs he can battle the warriors in the western conference finals for the next 4 years
If he loses: It won't hurt his legacy since the only thing that matters is the finals record, and nobody gives a damn if you lose before that
If he wins: He'll have a 99% chance of beating the team that comes out of the east since the only way the east has won in the past 7 years is because of LeBron
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Also, it will make the NBA Playoffs a lot more entertaining up until the finals when the western team sweeps the east.

If LeBron goes to the Clippers, Lakers, or Spurs he can battle the warriors in the western conference finals for the next 4 years
If he loses: It won't hurt his legacy since the only thing that matters is the finals record, and nobody gives a damn if you lose before that

If he wins: He'll have a 99% chance of beating the team that comes out of the east since the only way the east has won in the past 7 years is because of LeBron

Also, it will make the NBA Playoffs a lot more entertaining up until the finals when the western team sweeps the east.