Just like any technique, fishing is all about increasing your odds of catching fishing. By using planar boards you are doing this. This is not to say that you won't catch fish when not using planer boards.
Think about it. How many times have you been fishing all day with the best equiment and techniques and still haven't caught that lunker big fish. You come into the dock and there is someone on the dock, without a boat, fishing with a Canadian Tire special rod and reel, and they show you a fish bigger than you caught all day. In this scenario you could argue why buy a boat if you can catch fish off the dock. Now who is going to say that. Of course a boat is a valuable fishing tool but you can still catch fish with out one.
Don't be afraid to try new things but what I will say is stick with what works for you. If you are catching fish simply flat lining, keep flat lining. Don't change when what your are doing is working.
Just another side note, you can still feel the strike when using planer boards provided you are holding the rod.
Cheers,
Mike