Do I need (package-initialize) before these lines?
If your version of Emacs (M-xemacs-versionRET) is older than 27, and you are using the built-in package manager, then you indeed need to call (package-initialize) before you can call on any installed packages, such as use-package.
From Emacs 27 onwards, package-initialize will effectively be called ...
It doesn't do anything you couldn't be doing without it; so the answer might well be that it doesn't improve performance at all. It could vary from user to user.
It does encapsulate some mechanisms (which you might already be using) for making good use of autoloading and deferred evaluation of code, in order to avoid loading libraries any earlier than ...
Thank you Ian.
I manually downloaded the eclipse file directly from the site, eclipse.org. Then, installed it using GUI.
Then, manually downloaded the eclim file from the site, eclim.org. Then, I could give the path
Also, installed emacs-eclim by cloning the git.
Now, the eclimd is not starting. I will post the ...
The package name is matlab-mode but the provided feature is matlab. Have a look at the very end of that source code file.
According to use-package Manual you have to get that right.
So your use-package declaration should look like this:
'("\\.m\\'" . matlab-mode))