The choice to install an SYE should be made by two factors. One is driveline angles and the other is when the suspension is fully slexed up or down how much of the slip yoke on the front of the driveshaft is still on the tail shaft. Many have dropped a driveshaft on the trail. So when you lift you need to decide the need. There are many ways to get the driveline angles correct without an SYE. Tcase drop is the most popular, 1" motormount lift is another could cost a few bucks. The other is to change the shim at the spring perch at the biottom of the spring stack which sets up the pinion angle.
89YJ 2.5L TBI, AX-5, NP231 SYE, Ford 8.8, Yukon Grizzly, Tom Woods Shaft, 33" BFG T/As, 4" lift, Warn VR10000s.
AF Jeep Club Tail #184