I see some code like this:
script.Parent.MouseButton1Click:Connect(function(Player)
end)
Where do they get this player parameter from? When you type out an event, it tells you the parameters, if it has any. The GuiButton.MouseButton1Click has no events.
What these people need to know is that if an event by default passes the player as a parameter, it’s a server side only event. Take for example, the RemoteEvent.OnServerEvent event of RemoteEvent.
Do these people not know that they can just use Players.LocalPlayer to get the player (since these scripts are local)? The most common mistake is using LocalPlayer in the server, and just doesn’t make sense they stop relying on LocalPlayer, and just add a parameter because they feel like it.

12 comments
How is this a question?
It is, since it has a question mark and I asked why does this happen.
It is a primarily opinion based question. If a person feels like putting it, let them be. Maybe tell them that they don't need to put it. Creating a post and asking opinions will not solve anything.
No opinions here!
I’m just asking why people do it, no opinions.
What I am saying is that this is not a question. Maybe create a blog post or a forum post regarding the topic.
It is. It has a question mark, and it is asking why do people do _______? End of argument.
This is not what the website is for
Have you not read the guide to asking good questions?
I asked why do people do _____. Now shoo.
You should stop false claiming my question, it was a question that complied with the rules. Sorry your player parameter adding to the MouseButton1Click event self is triggered.
I'm sorry to say incapaz, but this "question" along with your last 3 questions just seem more like a form of bragging than anything. I can understand if seeing this in a script can upset you, but you have to realize that, at the end of the day, it just doesn't matter. People will be ill-informed about certain things, there's nothing you can do to change that.