Selling by subscription offers many advantages over one-time sales.
Sell by subscription will provide you recurring revenue. In addition, customers are more likely to continue paying for their subscriptions than to return to purchase your products/services. This means regular and predictable sales. All without any additional sales effort needed from you.
Subscription selling is also more suitable for customer retention. Customers who subscribe are more loyal than those who buy your products/services on a one-time basis.
Finally, you should know that subscribers are also more likely to recommend your products/services to their friends and family. Thus increasing your potential customers without having to initiate additional marketing actions.