A few years ago my dad was trying to kill trumpet vines that were taking over the yard and growing up the cherry tree my mom planted when we first moved there years before. He sprayed the whole area down. Killed the beautiful cherry tree and not a single trumpet vine. . Mom had just passed away the year before.
I just had the same experience with my Round Up spraying neighbors. They were trying to kill trumpet vine - instead the over spray took out my black raspberries! Of course the trumpet vine remained healthy.
One thing I see time after time after time. People w/ horse farms put weed killer down along the fence line. They don't want anything growing there because it makes it easier to mow. Only problem being, anything w/a really long tap root doesn't die completely. The top may, but that's it. But, the grass and clover will die. W/them gone, the weeds more or less just move in and take over. Plus, in any areas where there is nothing growing, they get a really heavy downpour, and then they have erosion. I can understand not wanting something tall along the fence. But IMO, they'd be better off pulling the weeds, and encouraging clover to grow instead. It will stay low, still look nice, and hopefully, choke out the weeds and stop erosion.
My sis has a hedge along two sides of her fence. Over the years wild cedar trees sprouted in the fence line and the local government comes along and "tops" the cedars to make it easier to see along the roadways. The result looks like a nice hedge.