What are beneficial about wraithguard?
Essentially, they are a very durable scoring unit (when fielded in squads of ten and led by a Spiritseer), which work very well in mixed lists at pinning opposing units in combats, or holding objectives/fortified positions, but they are rather expensive, so you do end up having to build the infantry section of your army around the units of Wraithguard if you go down this route.
Starrakatt and other members of the Iyanden POC are the best people, however, to answer this question, so I will leave furhter comments to them.