There's a reason websites put share buttons in prominent places. You need to capture that interest in the moment; forcing users to scroll around to find the button, as trivial as it may seem, reduces engagement. If you're using your profile URL to link to YouTube, you're hiding the share buttons and leaving subscribers on the table. Whether it's a political ad or a web series, you want as many eyes on it as you can get, especially in the first 24 hours. Subscribers are opting-in to get notifications of your new videos; you should want to make that process as easy as possible.