The main benefit I see is taking 2D plans, and being able to mark them up in the field, or on the go.
I can see this being beneficial if you have guys that go to the field to inspect, or supervise, and there are problems in the field to relay back to design teams. If your field guy is CAD savvy, he can also edit the drawing pretty easily on the iPad/iPhone (though obv the phone is a smaller screen) and when the drawing is shared, the recipient can 'step' through every change, with a detailed summary of the changes made. "object moved +2.00 X, -12.25 Y" for example.
You can open up pretty large drawings and navigate very quickly and easily. There's not much lag at all. It appears to me that it takes a quick snapshot of the drawing at the current zoom level, and displays a raster image of that area. When you zoom in it zooms in on the raster image, so as you zoom, you see the enlarged pixels and artifacts inherent with a blown-up JPG, for example. Then after a noticeable fraction of a second it regenerates a new raster image at the current zoom level. It's a small fraction, I just meant to say that you see it happen, though quickly.
I haven't messed with any of the tools other than selection tools. It's kinda neat how it has the same crossing window style of selection method, though now using fingers or stylus instead of the mouse cursor.
It's quite basic, has limited applicability, and -certainly- nothing to worry about getting if you don't already have a machine for other reasons. A pen and paper will still work, but I can foresee this application improving efficiency quite easily. I haven't checked to see how easy it is to flip back and forth between drawings, though.
It's probably 6 of one / half dozen of the other, as the pro/con list goes, when compared to pen/paper... and pen/paper has no cost that incurred already.
It's a neat toy though for a -current- iPhone/iPad owner, but nothing to go buying machines for, obviously. I doubt I'll even be opening the app up unless they get support of 3D content.
