It’s great to link layers because say you start moving one layer around and forget you had it placed like that for a reason. If you have it linked, it will move all the linked layers when you start to move one of them. That cluster is just as you want it, but not WHERE you want it, link up the layers and move it around without having to hold the control button constantly. You can change the layer order of the linked layers but any moving, including re-sizing, will affect all the linked layers.
I recently found this setting and I LOVE it! It works better than using guide lines when I am trying to line things up. You can turn them on by going to the View Menu, Show, Smart Guides.
I couldn’t get a screen shot to show you what they do, but purple lines show up when you use the move tool and it shows all the ways your layer is lining up with the other layers. Lines go along the edges and the centers so you can see the different edges you could line up with. I absolutely love it! When you are using an alpha to make a title, this is a life-saver! Check it out!