Simply put, as a player if you win big, you don't win big. They cancel your bets or find some way to say they were wrong and you 100% definitely knew you had an edge (you can't just be lucky) and thus you lose all you're winnings.
SO THUS, DONT play on sites with house investments.
Why would you say such things?
Just-Dice ran for over a year and saw some players win huge amounts.
Just-Dice never reversed a single bet other than the ones made by nakowa with coins that we accidentally left in his account after he made a manual withdrawal.
Players get lucky all the time, and a reputable site won't reverse their bets when they do.
It's true that it seems like very few sites are capable of making a working copy of the Just-Dice model, but that doesn't mean the concept itself is flawed.
Whether or not a site has an "invest" feature, it's pretty likely the site has investors. Do you think coinroll is bankrolled entirely by its owner? Coinroll almost certainly has "investors" providing the bankroll, to whom the site owners are accountable. Just because they don't offer the opportunity to the public doesn't mean they don't have investors to keep happy, so I don't see why you would make this distinction.
A better rule of thumb would be "don't trust untrustworthy sites" - but that's much trickier to apply.
Edit:
I just read your 2nd post. It contradicts your first post.
Why say "don't play on sites with 'invest' feature" and then go on to say "JD is the way to go", when JD has the 'invest' feature, and in fact invented it?