Transform Quantizer add-on aligns objects or vertex positions to an orthogonal grid of definable size by quantizing coordinate values of elements to match the closest grid-aligned point.

Mainly useful in three situations:

1. Precisely align to a grid manually placed elements with "eyeballed" positions or neglected precision
   
2. Round off positions (rotation or scale) values to a definable precision appease your "OCD"
   
3. Fixing float point precision issues by cleaning up values (1.9999 becomes 2.0 or 1.00003 is forced to 1.0)

Supported element types are

1. Objects - Position XYZ , Rotation XYZ, or Scale XYZ
2. Mesh Vertex - Position XYZ
3. Curve Vertex - Position XYZ , optional inclusion/exclusion of Bezier curve handles

You can precisely align position rotation or scale of element to the closest value of a defined precision value. The practical consequence is that elements coordinates become aligned to a grid of adjustable spacing by defining a precision value.

Use it to clean up models or scenes that have rough or approximate positions resulting for manual placement, eyeballing or neglected precision.
Often used in architecture or when the "OCD" kicks in and you jut don't want eye-balled or rough values.

Fix float-point precision issues introduced by some operations or importing from other software. These manifest in the UI as values that look like 3.999999 or 12.000000000001

Independently adjustable quantization values for X, Y or Z axis, quantize object position, rotation and scale, mesh vertex position for X, Y and Z axis in Edit Mode, and bezier curve vertex positions for X, Y and Z axis in Edit Mode, optionally including or excluding bezier curve handles.

In the above example only X and Y axis position are quantized, leaving the Z values as they are resulting in a still smooth surface.

Disclaimer

The addon only does a purely mathematical rounding of values, it doesn't try to "be smart" about it. You may some times get overlapping objects or "missing" grid spaces. If you get "wrong" results those have most likely to be fixed manually, either before quantizing by manually moving the objects closer to their desired final position, or afterwards by snapping them into place.

If you just to distribute existing objects into a grid-like precise array from scratch first, check out the Distribute Objects Addon