Daystar supplies two spacers, in order from bottom up, you have-coil, bottom spacer, stock plate, top spacer. The bottom spacer preloads your coil, the top spacer extends(pushes) your strut down aprox the amount of the spacer thickness. This causes the same effect like the suspension extending downward. In normal driving, the suspension travels up and down but returns to its normal place which the cv axle/boot is stright. With the spacers, the suspension stay extended and the cv boot angles. When it angles it is sort of tightens the pressure inside the boot. May not look like it on the outside but it does to a degree. You will see the noticable angle with the cpacers. Over time it will leak grease. Those high angle spiral aftermaket cv boot that supposed to work better, well didn't last as long as the stock one. But who knows, maybe nissan used better cv boots then toyota.
I'm not saying don't buy it, it's your choice. I loved the way mine rode with the spacers but wasn't worth it in the long run. I had it on for 12k miles. Mine started to leak after 5k miles of use.