depends. The psychoactive part of the plant is concentrated in the trichomes, which appear on the flowering tops. These are tiny hairs, which have a sac with the resin atop.
If a plant is fertilized, then all the energy goes into producing seeds, rather than trichomes.
(There is no accepted consensus as to the evolutionary reasons for this feature. Given the Himalayan origins of Cannabis species, it has been suggested it's a protection from UV light).
Therefore, drug producers try very hard to prevent their female plants getting fertilized - they try and keep them without seed. And Spanish for "Without Seed" is "Sinsemilla".
However, some people also like to breed their own strains of cannabis. For this (obviously) male pollen (and therefore plants) are needed. Once the pollen has been gathered, the plant has no use.
The fact that I know all of this show what an utter farce the past 44 years have been.
Incidentally, it's fucking anti social to dump any waste material. But even worse when it's something which could have easily been composted. If I caught the culprits, I'd give them a pass on the drugs, but cut their balls off with a rusty razor.