When collecting or acquiring plant material the first place to consider are the characteristics of the plant you want to preserve and if propagation is best done by seed saving or a variety of methods to clone a plant. This of course, depends on the species, the qualities you want, and the time, energy, and money you want to invest. Often times there is not one “right” answer, but a specific answer to your specific context.
For example, if we consider Honey Locust a desired species in our Forest Farm, you might take the time in late fall to collect some pods and store them for growing the following season, or purchase whips grown from seed. This strategy is perfectly appropriate if you are ok with variable yields on pods and thorns on the trees, for example if you were more interested in the nitrogen fixing capacities, early food source for bees, or firewood yield from trees, or wanted to use a row as a living fence.
However, if you want Honey Locust for animal fodder, or will be growing the trees in areas that will also be used by the tractor, you’d likely want to invest in thorn less and high yielding varieties that you could then take cuttings from and graft into regular rootstock, from seed you started or purchased. In the end, you’ll need to collect or purchase seed either way, and potentially graft if you want specific qualities in your offspring. The exception comes when the seed of a plant remains “true” to the parent.
And, in some cases, like with Rubus spp (Raspberries, Blackcaps, etc) there is really no choice in propagation strategy; its easy enough to divide the root system or dig up suckers which pales in comparison to the arduous and impractical task of saving and starting the seed.
When you buy cultivars keep in mind that the added cost you are paying is for the time and energy someone else put into growing, selecting, and breeding plant stock. We are fortunate to have this legacy of human effort on many plants of interest to the Forest Farmer. Others, though, like Black Locust and Lions Mane Mushroom, for example, have lots of development work ahead of it to improve yields and other qualities.