It's a lot easier to say no dog allowed in the park than to say "only good well behaved dogs allowed".
You have to get a lot of things right when swapping to 650b wheels. As others have said if you have rim brakes they will not work. You might be lower to the ground where you pedals might hit on some turns or terrain. Seems like most 650b rims tend to be wider ( moutain/gravel bike ) so maybe the tires or too wide. Seems like a lot of 650b wheels have 9 Spd cassette vs 700c wheels that have 11+ speeds. Of course you can get around all that but it's a lot easier to say it's not recommended.