I very, very rarely sell my images. I own everything I create and issue a "Rights License" giving the Client Non Exclusive rights to use the images. This allows me to continue to use my images as I see fit and restricts the Client from uses I don't approve of. (selling them or using them in a manner I would not support)
If you sell your rights to the images, they're gone. Like you never even created them. No portfolio use, no use in marketing materials, no possible future resells, etc. Gone.
The only time I've issued Exclusive Rights to my images are for a certain Client who uses some images as legal evidence in a court trial or legal action. They're sensitive in nature and wouldn't be of any future use to me anyway. This is rare though, as 99.999% of what I create, I own. Forever.
Plus, my Rights License also expires after 5 years. You could, issue Exclusive Rights for a short period of time, like 3 months, 30 days, whatever. An example of this would be if you happened to capture incredible images/footage of a VERY noteworthy event, and a major news organization wanted your captures to "scoop" the others. Give them Exclusive Rights for say, 2 weeks. That's all they'd really need once they broadcast it anyway. FOR A VERY PRETTY PENNY!