Lightroom has very similar controls for rotation in two different sections. First, in the Crop & Straighten tool:
Second, in the manual section of the Lens Corrections control:
The Crop & Straighten Angle tool has an adjustment range of ±45°, while the Lens Corrections Rotate tool only has a range of ±10°.
What is the difference between these controls, and when should one be used instead of the other?
The Rotate bar under the Crop & Straighten tool is used to rotate the image the way you like. For example when you were taking a landscape photo of the sand, sea, and sky, you didn't place the horizon in a perfect horizontal line and you want to fix that. You want to make the horizon perfectly horizontal so you can use the rotate bar under the Crop & Straighten tool.
The one under Lens correction is responsible to correct distortion caused by the lens manufacturing. In the profile tab you can select the manufacturer of your lens and an automatic profile (fixes) will be applied to your photo (if Lightroom has your lens profile). Note that the sliders in the Manual tab are used to give you more control to do further fine-tuning.
Exact differences are:
The Rotate bar under the Crop & Straighten tool is used to rotate the photo. Using the slider you can go from -45 to 45. You can rotate the photo clockwise or anti clockwise in 90-degrees increments. The axis of rotation is the center of the crop rectangle.
The Rotate bar under Lens Correction is used to correct camera tilt. Uses the center of the original, uncropped photo as the axis of rotation.
Please check Adobe Photoshop Lightroom 4 Guide for both here and here
From my experience, these two features produce the same result. And since, as I haven't experienced any "real" lens distortion that rotates my images, I think you can use them however you want.
This is how I use it :
if your picture is not straight and only needs a few degrees of correction, if it's slightly crooked, then use "Lens Correction > Rotate", use the horizon or any vertical line to align your picture properly. That's considering you took a picture that really should look straight.
if you want to rotate your picture to "produce an effect" (like tipping your horizon at 45 degrees), you'll use "Crop & Straighten > Angle"
The best reason for using these tools this way is that if you have 200 same shots (say aerial), and only a few are slightly crooked, then you should fix the crookedness only for those pictures (using Lens Correction), and then if you'd like to batch rotate all of them (the 200 !) at 45 degrees, use Crop & Straighten (and Synchronize). That way, all pictures are treated equally regarding the 45 degrees, and the ones that were slightly tipped are corrected using some other parameter (i.e. "Lens Correction > Rotate").
If I only have one shot to deal with, I generally prefer using "Crop & Straighten" because it has a grid overlay.
