Decks come in varying sizes for both the width and length of the deck. A smaller deck in both width and length will be more lightweight and aerodynamic and make your park tricks easier to pull off. A wider deck will be more comfortable and make most grinds much easier since you’ll have more wiggle room to lock into them. A longer deck will again give you more footspace, which will feel more comfortable and affect the ‘balance’ point of the deck for grinds and manuals. For deck length, the main factor is personal preference and riding style.