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Hello @aarcee, thank you for your reply!

I believe diversification is a free lunch and it's useful in almost all circumstances.

Granted, it's not efficient if you are perfect in your investing: it would not have helped Bill Gates to diversify away from Microsoft shares (and some famous investors mentioned they have concentrated portfolios), but for most of normal investors it has always the below benefits:

  • reduces idiosyncratic risk specific to the single investment
  • reduces volatility
  • by reducing vol increases returns over the long run

So I would say it's advisable to all investors who have a long term approach. For speculators and for betting, it's also good to have it but much less that for investors.