From SmashWiki, the Super Smash Bros. wiki
Briefly winds back before rushing forward, engulfing his right foot in flames while announcing “Falcon Kick!” Compared to Melee, the move has less utility due to how it does not grant Captain Falcon another midair jump if he has used one earlier and how the grounded version is weaker in terms of knockback and damage potential. The slower mechanics of the game result in Falcon Kick being even easier to punish, and as a result, the move’s potential is relegated mainly towards recovering from a high distance or taking advantage of opponents in lag. Examples of how he can utilize the latter is by punishing Meta Knight’s Mach Tornado in lag. Falcon also try to use it as a situational approaching tool to catch unaware opponents. This move is better suited at higher percents, as opponents may attempt to play more defensively and will be caught off guard by its power, enabling Falcon to potentially edgeguard or land a finishing blow.