Short answer: Don't be worried. For most applications there won't be an issue.
Long answer: If you look into the framework level code a bit and see how laravel actually handles the request when you call Auth::User()
you will see that for the authenticated user every request goes through SessionGuard which immediately returns the user instead of making a database call.
https://github.com/laravel/framework/blob/5.6/src/Illuminate/Auth/SessionGuard.php#L122
public function user()
{
if ($this->loggedOut) {
return;
}
// If we've already retrieved the user for the current request we can just
// return it back immediately. We do not want to fetch the user data on
// every call to this method because that would be tremendously slow.
if (! is_null($this->user)) {
return $this->user;
}
So your first hit is going to make a trip to database and the subsequent request should just return from session as shown below. You can validate this by enabling Database Query logging in Laravel and see what queries are making trip to the database. For further info on Query Logging you can read the doc per laravel veersion or this conversation.
From a performance standpoint, unless you are going to have thousands of concurrent users hitting the site on a DB heavy application then DB connection is going to be the least of your problem, You will run into other issues first before the database gets bogged down. I don't have much of a context so I'm making assumptions. You can always throw more commodity hardware or move caching to another datastore such as MemCache or Redis if you start to notice performance degrading. The reason you've chosen Laravel (PHP) is for speed in development and not necessarily for performance.
But it's great that you are keeping performance in mind and you're thinking through these things as you build your application.