Maimonides explains that the prohibition of “rounding” prohibits the removal of sideburns, by razor,
Even though sideburns are enough to satisfy the Torah requirement of peyos, many Jews grow their peyos long as a way of emphasizing the commandment. Some will curl their peyos, while others tuck them behind their ear. It’s just a matter of individual taste, or communal custom.
Hair is also a symbol of vanity, a preoccupation of how one looks. The prohibition against cutting off the peyos reminds a person to de-emphasize his looks, and instead depend on intellect and good character.