Have people been using 3D printing to genuinely create a number of needed objects in their homes, and if so, what? Or is 3D printing better for special niche interests like art projects, home engineering projects, etc?
Have people been using 3D printing to genuinely create a number of needed objects in their homes, and if so, what?
Yes, but in a very limited sense. If there is widespread demand for an item, then it will always be available from stores. This is basics economics: if there is enough demand for something, somebody will step in and provide the supply. The store-bought alternative will almost always be of better quality and relatively cheap.
3D printing can be useful to create a niche part that is needed but not readily available, such as replacement parts for appliances long out of production. This unfortunately takes a lot of time since you need to make a 3D model of the part yourself, which also requires considerable skill.
Some examples of items that I made for my home:
Custom brackets to hang blinds when the store-provided ones did not fit my window.
A special mounting bracket to more easily hang a ceiling light panel.
Replacement wheel for a vacuum cleaner.
Cover plate for a deprecated telecom socket.
Fix for a broken clothes drying rack.
3D printing can also be used to create "trinkets" such as custom vases or similar objects.
I would say 3D printing is a bit like woodworking as a hobby: it is a skill that can be used to make genuinely useful items, but going to IKEA is a perfectly viable alternative.
Or is 3D printing better for special niche interests like art projects, home engineering projects, etc?
It is ideal for this. I do not know of anybody who has a 3D printer specifically for home use. However, there are many hobbyists that use 3D printing for another primary purpose that occasionally find their 3D printers useful around the house.
3D printing is a tool. A really versatile one. I have myself used it in various applications:
I have broken a couple of appliances in the past and then made spare parts with my printers, skipping on delivery and full replacements. The hanger in the wardrobe got a replacement disk, the vacuum with the broken hinge got the break briged and a couple of other items have gotten simple but effective custom spare parts.
Be it taking the Colosseum into the class or a miniature of a Roman Castra, a Danish longhouse, it is different to have a picture of something or allowing to turn the item around and look at different angles.
And there are ways to teach physics or geography with it too! For example, a simple sextant can be printed and then used to determine the longitude of your school, or you print the fixings of a Blackburn Pendulum or a harmonograph and ask your students what influences the patterns of the complex shapes that appear.
In languages, the use larger (~30 mm) dice with the forms (for example in Latin: ego, tu, is/ea/id, nos, vos, ei/eae/ea) or tenses generates questions for the students in training and self-study.
And then there is the use to make custom boxes to transport all the learning aids.
Cosplay & LARP
I have printed decoration and art pieces for Cosplayers and LARPers that would take a lot of handiwork to make otherwise. Be it helmets, masks or shoulder armor, 3D printing allows manufacturing complex items for such.
Engineering & Tools
I have not used it myself a lot, but on the 2016 SMM, I had talked with a fluid dynamics laboratory that used (miniature) FDM prints of static propellers to test an evaluate designs in water basins.
Similarily, on the 2018 didacta, I had seen projects by several universities to combine engineering with education and getting basic training in engineering into schools as extracurricular activities.
There are numerous tools for spacing and such that you can easily make or adjust to your needs. A friend of mine works in wood professionally, and they printed themselves drill-jigs for parts they repeatedly use.
Art & Decoration
Here 3D printing can shine, and I have made pure decorative objects too.
3D printing is especially useful for creating replacement parts for things for which it would otherwise be difficult, expensive, or impossible to obtain a conventionally manufactured one. You may have seen in the news recently the story about 3D printing being used to replace hospital ventilator valves that were not available in time to save patients who needed them, and that normally cost \$11000 from the manufacturer. But the same kind of thing applies to regular household items too. For example, I've replaced broken wheels on my child's toy cars, a broken windshield washer fluid coupling in my car, and various similar things. I'm also planning to replace broken plastic wheel bearings in my vacuum cleaner (the manufacturer's design was atrociously bad and I'll probably adapt it to use real bearings with a 3D printed adapter), a window switch in my car, and lots of other things I can't remember at the moment.
Of course you can do craft and hobby things too. I don't think this really calls for examples/evidence.