Does PreloadAsync reduce lag?

Might be a dumb question, but I'd like to know.

Think about it this way:
Without loading your assets beforehand:
If the client is interacting with an asset for the first time, ROBLOX renders the asset in front of the client. This means that if the client is interacting with a complex asset for the first time, the asset will slowly be rendered in, instead of just appearing. This technically may cause some lag on older computers.

With loading your assets beforehand:
If the client is interacting with an asset for the first time, ROBLOX has already rendered the asset for the client, so it will appear straight away. If the client is loading all of the assets at the start of the game, it may cause some lag. However it can slightly improve performance and may make the game look more professional overall in a game.

Really, you should only use it if it is necessary, but it is your choice.