Yes and no. Obviously, if you block a bot and they honour it then they will not index your forum but the bots that are being blocked here aren't necessarily 'good bots' that you would want to allow access to your forum in the first place.
It's important to make sensible decisions when it comes to bots and their access. Blocking Google will prevent your forum from being index in the future so if Google is visiting your site too much, you might need to look at other methods over basic banning so to speak.
Purchase the 
also not sure about Facebook and Apple, if there can be some drawback but probably not.