Generally speaking, if you buy a size that is larger that comfortably fits you, there are very few tweaks you can make in it so it’s better to you. On the other hand, if you have a fractionally smaller size, you play with a few variables and feel much more comfortable. The only exception would be in cases of very short people, where buying smaller than good size may become inconvenient on low speeds while turning, and hitting the front wheel with their shoe.