Photography reflectors are usually white,silver or gold coloured sheets that are positioned to reflect light onto the subject. They are great for filling in shadows , highlighting a model’s hair, etc, but they aren’t always easy to carry around with you. They tend to be either large and solid sheets, or fabric in a springy circular frame that can be twisted into a smaller disk and stored in a carry case. Neither is small and light. Consequently there will be times when you could use one outdoors,but you didn’t bring it with you because of the weight and inconvenience.
Space blankets are ultra-lightweight plastic foil blankets designed for use by long-distance runners, at charity runs and as emergency thermal blankets for outdoor enthusiasts. You often see runners at the finish line wrapped up in one as the cool down. They fold up into a tiny package smaller than a mobile phone, weigh next-to-nothing, and have the bonus of also being a valuable item in your First Aid /Survival kit.
Just unwrap the blanket, open it up, hang it/ pin it / get somebody to hold it where it is needed, take your shots, fold it up again and carry on. How much easier can it get?