If you feel inspired to do so, I think that picking up trash helps others to see the world as whole and healthy, without the distractions of others' rubbish.
True. However, the downside of that is if everything around us looks nice, we can easily forget that the earth isn't whole and healthy, but is in fact sickening and dying from what modern civilization is doing. In that respect, it could be a very good thing (to prevent complacency) if everyone had to see the true, naked results of the modern way of life, rather than shuttling it all off to landfills and toxic waste dumps.
I believe that every inch of the earth is sacred ground, and that picking up trash doesn't "clean" the earth, it just cleans that spot by moving the trash to another place. Thinking about what is best for the land, I've concluded that it is slightly better to keep the trash contained in a place that is already contaminated with it (a landfill) rather than having it dispersed over the landscape and affecting wide swaths of it (although at a MUCH lower level). I think the difference is pretty slight, however.
The whole concept of "waste", of "throwing something away", is fictitious (delusional). There is no "away" on a finite planet, and there is no "waste" in the cycle of life. Everything natural is food for something else. In all of earth's history, only modern humans have broken the cycle by creating objects and materials that take countless years to break down to the point (essentially, the molecular level) where they can once again become food for the cycle of life.