Prior to the 1970s, the most common man-made anchor was the piton. However in more recent years canyoneers have switched over almost exclusively to bolts. In some extremely rare cases, canyoneers may use pickets.
Some landowners, like many National Parks, do not allow people to install new man-made anchors.
If installed correctly, man-made anchors are extremely safe. They are generally long-lasting and have minimal environmental impacts if installed correctly.
Bolts can be difficult to verify that they were installed correctly. Because of this, and other reasons, we prefer to have multiple anchor points.