In 1985, Minolta became the first company to produce a body-driven autofocus 35mm SLR -- the Maxxum 7000 -- and with it, the new A (also called Alpha or AF, replacing the incompatible manual-focus SR/MC/MD) mount became the camera system to have. Unfortunately, lawsuits soon followed: Exxon sued over the typography of "xx" in Maxxum and Honeywell (Pentax) sued claiming the autofocus technology infringed on their patents. It's a long story, but that began a slow fade; Minolta became Konica Minolta in 2003, finally giving their camera business to Sony in 2006. Although A mount is now second to E for Sony, by my counting, more autofocus lenses have been produced in A than any other mount, so there are plenty of reasons to want to adapt A-mount lenses... and there are various adapters available -- including the LA-EA1/2/3/4 from Sony itself.
Ok, so why 3D print this one? Because we can seems like a decent answer -- this is an easy print in 2 pieces, the adapter itself and a little locking pin. Certainly, this adapter fits nicely on a Techart Pro LM-EA7 autofocus adapter and uses only about 12g of the 700g drive limit for the LM-EA7. It's great for manual A-mount lenses. The catch is that it doesn't yet incorporate an aperture control for autofocus lenses... which are the vast majority of A-mount lenses. Hopefully, I'll find a good way to implement that soon... but the LA-EA4 adapter already implements aperture control and native autofocus using those lenses on Sony E bodies, and I own an LA-EA4 as well as an LM-EA7.
The last two photos were taken using the LM-EA7 on a Sony A7II, autofocusing a manual-focus Samyang (Opteka) 85mm f/1.4, both shot wide open. In fact, it's the only manual A-mount lens I own. Exceptionally smooth bokeh from that lens, but that super smooth transition to out-of-focus makes it hard to focus manually. By itself, it also has a rather long minimum focus distance, which isn't a problem combining manual focus with autofocus tweaking by the LM-EA7. I think this lens by itself is enough to justify making this adapter, although there are some other great manual lenses in A mount from companies including Samyang and Zeiss.