When you send payment requests via text message or email, they can get sent to junk folders, or overlooked in an endless stream of text messages.
That WILL NOT happen when you process payments through the app because:
(-) Special Request payments offer a banner notification in the app that doesn't go away until a client has responded, so your clients won't overlook them.
(-) Subscriptions can auto-bill on a daily, weekly, monthly, or annual basis, so once a client signs up for a subscription, it's on auto-pilot for the duration of the plan.