Lots of people say this, I think due to the hidden "secret" bunkai of Karate kata of hip throws via low block, etc. As I understand it though from deeper reading, the founders of Karate never designed the kata to have those movements, they've been later "discovered" (more likely made up). Whether that's true or not is up for debate, but surely if Funakoshi Gichin Sensei had more hidden applications for all the movements, he'd have put them in his books so they'd outlive him as he did with his techniques and philosophies.
At least Kukkiwon Taekwondo is more honest, there are no hidden purposes to Taegeuk. The moves are as described, a low block is just a low block. The purpose of poomsae practice is long-term (life-long) training, balance, co-ordination rather than practicing a secret set of Taekwondo self defence applications that you need special practice to unlock. They were never designed in there in the first place.