If I change a sprite’s size by .001, will it work? What about if I change the x value by that much? Is it different for different attributes?
proabably whatever the limits of the JS numbers (which are 64-bit IEEE-754 floating-point numbers) are
Snap! keeps its internal idea of all those attributes in floating point, which is important because a large number of small changes can add up to something visible. So, yes, you can make small changes and eventually they’ll have an effect. But of course the resolution of the screen means each small change is invisible, until suddenly they add up to one pixel (≈ one “step” in the MOVE block (or maybe ½ step for very high resolution monitors)).
Some visible attributes aren’t measured in units of length, though. Most importantly, rotation by less than one degree can have a visible effect. Graphics effects such as Mosaic and Pixelate have underlying small-integer values that are scaled up so that the SET _ EFFECT block has a reasonable effect in the range 0-100. (In the case of Mosaic, it seems by experiment to be that if you want n^2 small copies of the costume you use a value of \max(0, 10 n - 15), which is a little weird since it’s an affine function, not a linear one.)