Straps and hooks are used to compensate for grip or on lifts where grip maybe the limiting factor. In strength training they are more commonly used with pulling movements such as deadlifts, rows and chins, and power movements such as snatches and cleans. Wrist straps will allow you to use more weight when grip is the limiting factor.
Concerns to keep in mind with using Straps and Hooks
The overuse of straps and hooks can be the underdevelopment of the muscles involved with grip which are the majority of the forearm musculature which is commonly a weak point for beginners therefore straps and hooks should be avoided and only used sparingly if at all for more advanced individuals.
The act of griping the bar also assists in shoulder stabilization. The stronger the grip lifting the load the greater stability that will occur in the shoulder.
Possible benefits of using Straps and Hooks
Maybe the only benefit for using straps or hooks is to allow greater loads to be lifted when grip is the limiting factor. The risk of this may outweigh the benefit and should be used very sparingly as an overload technique rather focus on improving grip strength beyond what may be needed for a given lift. An alternative to using them is to use chalk or Hook Grip before resorting Straps or Hooks first.
Programming for Straps and Hooks
It is suggest that Straps and Hooks be used sparingly, and only in the heavier load phases of your programing but even then should be limited.