Im tracking the Players position and if the player is away from Parts they will be Parented to the ReplicatedStorage and if they come near to the Part it will Parented to the Workspace.
Do i need to parent it to nil or replicatedStorage to prevent Lag?
Just parent it to replicated storage, it would lag on both.
Setting an Instances Parent to nil is the equivilent of using Instance:Remove() (not Instance:Destroy()), You Arent Destroying the Instance, but the game wont Render it as it has no Parent, But the game will still have to keep track of most of its Properties.
ReplicatedStorage is a Shared place for both Server and Client, and would be more ideal, However, if you are looking to Secure it from Exploiters, you might need to place it in ServerStorage
either way, the game will have to Remember its there.