@FO just pointed out this trick. 

Sometime, it may feel a lot easier to select all parts in an area by dragging a box. 

In xHighlight, when you left-click and drag, it rotates the model by default, instead of drawing a box. 

Now you can press the left mouse button down for 2 seconds, it'll learn you are trying to box-select. 

Then drag a rectangle and everything in it will be selected🎇

One quick note, any parts touched by this box will be picked up. They don't have to be in the box completely.