I hate the things. If you’re trying to get rid of privet, let’s just say that you have job security. Dig all you like, it will pop up elsewhere, not the least because wild birds enthusiastically poop out its seeds everywhere. And the smell - when the flowers first open, there’s a delicate, sweet scent, but it quickly turns to over-the-top rotten/sweet that follows you everywhere.
And what fuzzi wrote is the description of an invasive plant: originating from elsewhere, generally another continent, that no longer has the predators (herbivores for plants) and diseases that keep it under control where they co-evolved in its home territory. So in its new home, it has little or no competition to keep its numbers and size under control. Now growing with few natural controls in its new homeland, it out-competes native plants for sunlight, for water, for space, and for attention from pollinators, while at the same time generally of less quality than native plants for the native animals that depend on them for food, shelter, or nesting.
It goes in reverse, with North American plants like Canadian goldenrod, prickly pear cactus, and the dreaded honey locust tree (in addition to various animals) now invasive on other continents.
- Most exotics (species from elsewhere) are pretty benign. As far as I know, Japanese azalea hybrids for instance aren’t trying to take over the world. But Japanese (and Chinese) wisteria; hoo boy.