A tip cutting can be a piece of a plant's stem or of its root. My experiment was done using the tips of an oleander plant. Most cuttings are stem pieces; and after the stem is cut to the desired length, all but a few of the leaves are removed and often the very tip of the stem piece as well (routine removal of the tip encourages early branching of a new plant).
Tip cuttings are mere 'pinchings' from the ends of stems so that, ideally, when cuttings are taken, the tips of each cutting can provide an additional opportunity for a new plant. In other words, you cut a piece of stem say 7" long. You remove all of the leaves from the piece of stem closest to where the stem was attached to the plant, leaving only a few leaves; and then you pinch out the very tip of the stem.
The bared end of that piece of stem, the piece with no leaves, is then stuck into soil, kept sheltered, and watered; and eventually should form its own roots, thus becoming a new plant (often before sticking the cutting into soil the bare end is treated with a rooting hormone).
In the past we've discarded both the leaves we strip from the stem and the tip of the stem we've pinched out. Often that tip has flower buds and those are removed because a rootless piece of stem will spend its energy on getting the flowers open rather than on forming roots.
If I wanted stem cuttings for their flowers, I'd cut the damned things and stick them in vases in the living room. What I'm doing here, on the other hand, is all about facilitating the making of new plants.
Using both the longer stem cutting and the formerly-trash tip of that stem as a second cutting gives us twice as many opportunities at propagation: the piece I cut on purpose and the piece I used to throw away.
In this example I never actually cut anything but literally pinched off the final 2" or 3" of tender growth from ends of some branches of an oleander plant with a deep pink double blossom.
After removing a flower-bud sprout from each of them (another pinch), I rinsed and then stuck the pinchings, plant end down, in a small clear glass jar with just enough water to cover the ends...and put the jar in a north facing windowsill and waited.
And then I waited some more.
Every few days I would empty the water, rinse the ends of the pinchings, and put enough fresh water into the jar to cover the ends again. There's a reason, related to oxygen's beneficial effect on root formation, for changing the water rather than simply replacing what evaporation takes.
I hadn't made a note of when these went into water but after what seemed like a long time I noticed the beginnings of roots, small enough to not to even be visible in the first picture.
And then one day there were enough roots to remove these babies from their water world and plant them in very friable soil. All five pinchings had rooted; the two that had the least root system shared a pot.
The cutting with the least root system didn't survive and a second plant succumbed to cat intrusion. The remaining three cuttings aren't cuttings anymore but tiny plants with a measurable amount of new growth.