Ease of use, faster, full control over the footage, 100GB of storage, the list goes on. I did not make a site just for the footage, I created my business website with sample footage, my portfolio, list of services, blog, gallery etc. It just happens to also have plenty of free space, so I also store footage for customers there. They get access to the link for 7 business days then I remove the footage from my site. It's just easier for me to do everything all in one place. Also, with your own site you can integrate PayPal or other payment processors into the site so that once the customer pays the invoice they automatically get a download link to their footage. Last but not least, I think it looks more professional when everything points back to your website vs having a gmail email account, dropbox for footage, etc. etc.