When printing the rasterization engine does quite many pixels. Thus it is not likely to generate a gap. A gap can still form from misalignment of plates but this would happen even if you would overlap because the rasterization process would still overlap the elements. That is unless you overprint
Printing aside, overlap is better for many software engines. Software engines do need to anti alias the edges. This process can be done with 2 methods:
- Computing mathematical coverage
Oversampling is computationally intensive, but is not very likely to cause a gap just like printing. Because its computationally intensive its often avoided.
So nearly all SVG and PDF renderers out there work with coverage computation. Coverage computation is prone to aliasing error because it guesses what the background color is wrong if you do not overlap. So when your client complains about white hairlines, you should know overlap would have helped. So the example form this post:
Image 1: preview of firefox. Source SVG: http://imgh.us/tris.svgz
Image 2: preview of firefox w overlap. Source: http://imgh.us/tris2.svgz
Downside of the overlapped art is that its easier to rebuild and modify should the client want to do so against your wishes. Also beneficial to you had the source gotten lost.
Overlap may be helpful if you need to share digital files with clients.