The stuff is designed to kill plants with broad leaves whether they be weeds or border plants. It does not kill grass. So if there is any drift on to the border it will kill plants there. Make sure that none of it does get on to your border plants.

I don't use it & it's not really necessary for a nice lawn. I use Scott's Turf Builder (I'm in the US). It's a fescue blend of various types of grasses so it will grow in either sun or shade. It's got lawn fertilizer & soil conditioner as well. It produces a robust healthy lawn that chokes out weeds itself. I just have to keep it mowed.

as Owd says any that gets onto the border plants will suffer.
My Oh did ours on Monday and I am just hoping he was careful. Mind you we still need rain to help dissolve it and wash it in. He had to use the hosepipe on Tuesday as the rain forecast didn't materialise.

If it isn’t washed in by rain it will turn your grass black. They say two days grace. I always check the weather first.

The moss and weeds turns black whilst the grass stays green. We had to water ours a second time as it hasn't rained enough here to make any difference.