When you ask an investor to invest capital into your opportunity you essentially are asking them for permission to manage their money. Investors typically do not have much information upon which to base their opinion of you - which makes it critically important that you approach them in a sophisticated, professional manner.
A Regulation D Offering will dramatically increase the sophistication of your transaction and your approach to soliciting investors. Investors will not typically invest into a transaction unless they feel confident about the capabilities of management. By using a Regulation D Offering you will approach investors with concise transaction structure, professional documentation, while using the proper process and technique for raising capital.
Remember - you never get a second chance at a first impression.