Uniballs are now very common on off-road vehicles and they're relatively simple devices that serve significant purposes in steering and suspension systems. OEM ball joints are typically used in pivoting suspension assemblies such as A-arms. They may serve well for stock applications, but the addition of larger tires and wheels with greater offset causes increased wear at the joints. As such, some aftermarket suspension assemblies use uniballs in place of ball joints, and off-road race vehicles use them more often than not.
Uniballs are favored for severe stress conditions over ball joints because of their superior strength and durability. They will simply last longer and hold up to severe use better. They also offer other advantages when compared to a standard ball joint. They are often capable of greater angular movement at the joint. Uniballs can also be mounted in double-shear, meaning you get increased stud-mounting strength. Should the joint ever destruct, it still remains captive, unlike a severed ball joint.
Uniball assembles consist of a cup that is typically welded into a component, such as an A-arm, plus the spherical bearing assembly that presses into the cup. Servicing worn components is done by pressing the bearing out of the cup and installing a replacement.