The closer you are to the equator, the more accurate use of a bounding rectangle will be. Near the poles, the bounding area becomes more trapezoidal, in the immediate polar vicinity, and at the poles themselves, it's technically a circle, so just checking longitude would make for a quick
test.
For a more precise, but rapid calculation, you can probably use rectangles up to about 60 degrees N and S, it's up to you how you want to address stuff beyond that. On the
Earth, most places of interest are probably below 60 degrees.
You can also use the rectangle test for a rough exclusion, then use a more detailed (slower) algorithm for winning candidates. Which algorithm you might use depends on whether the final bounding area is rectangular (more or less), circular, or something else and gets you solidly into 3-dimensional surface geometry maths.
All of the above are based on the idea that, given a point, you're trying to prove proximity to some other point or area. The actual question read more like "I want to find all points within this area", and since longitude and latitude are non-integer values, the potential number of answers to that question is infinite, allowing for arbitrary cutoff of precision.
If you're attempting to find the area (of whatever shape) is centered on a supplied point, you'd more or less turn the above suggestions inside out.