Retrieving A Portion Of The Input Data

Retrieving A Portion Of The Input Data
If you need to retrieve a subset of the input data, you may use the only and except methods. Both of these methods accept a single array or a dynamic list of arguments:

$input = $request->only(['username', 'password']);
$input = $request->only('username', 'password');
$input = $request->except(['credit_card']);
$input = $request->except('credit_card');

onlyとexpectの違いは？

Determining If An Input Value Is Present
You should use the has method to determine if a value is present on the request. The has method returns true if the value is present on the request:
ここらへんは分かり易い。

if ($request->has('name')) {
    //
}
if ($request->has(['name', 'email'])) {
    //
}
if ($request->filled('name')) {
    //
}