Which operations are expecting input in radians and which in degrees? Triggered by this question (unfortunately the OP didn't elaborate on the context), I'm puzzled now: which operations are done in radians and which in degrees?
In the 3d window all navigation is in degrees (presuming the Units selected for the scene are indeed degrees), but from what I read, internally Blender is using Radians, leading to some confusion when setting drivers, constraints, modifiers or texture mapping. So far I haven't run into any issues but I'm just trying to understand the logic behind it.
You can input a value in either radians or degrees by appending a "d" suffix (for a value in degrees) and a "r" suffix (for a value in radians) to the numerical value.

"1.5913513r" => in radians

"1.5913513d" => in degrees

For example, if you click the X-axis rotation button of an object to input a rotation value manually, and write "1r", after you press ENTER to commit the value the button will show 57.3º. Hovering the mouse over the button will show a tooltip saying "radians: 1.000000" (and 57.3 degrees is the approximate value of 1 radian).

You can use this when editing drivers, rotations etc. in case you prefer one unit over the other, and Blender will do the conversion for you.