You can download images anytime but you must apply your code within 60 days if not risk losing your rights to get these high quality images
Only for Standard images at the moment
You can stack unlimited number of codes for more images if you want too if you decide to refund them your rights to the image or images is revoked .
Images themselves can allow a business to increase there click through rates which is important factor in rankings in Google or simply allows you to increase the possible chance of your business or clients business for making a sale by you having attractive images on all your posts or pages.
Paying for images if you have big website can cost a lot of money per month or even day so if you have a need or desire for this type of images then buying it would make a smart decision overall and it saves you the hassle or getting them yourself