What is the point of doing onserverevent:connect(function(...)?

Basically, things that the server changes can be seen by all clients. But if a client changes something it'll only work for them. In some cases, you want the server to do something when something happens on the client, to accomplish this we can use RemoteEvents. This lets a client fire a function which the server can detect and read.

I'd suggest reading this article regarding the Client-Server Model, it goes quite in-depth when it comes to your question. If you have any further questions you can just comment on this post.