When Jigoro Kano formulated Kodokan Judo, he wanted preserving martial skills, martial virtue and martial history through the practice of forms while allowing for new ideas to develop through the practice of randori. When Gichin Funakoshi formulated karate, he thought that forms practice should define, rather than compliment, training. Modern Taekwondo stresses competition and claims that its patterns represent and preserve fundamental Taekwondo movements and strategies but they do not, nor do they demonstrate useful sparring techniques.
There are several sets of patterns used by Taekwondo schools around the world, such as the American Taekwondo Association's Song-am patterns, the Jhoon Rhee Martial Ballet, the Pyong-Ahn patterns, the Taegeuk patterns, the Palgwe patterns, and the Chang-hon patterns. Whichever set you practice, you should know its origins and its current purpose.