In architectural terms, a joint between two things – for example, between a sidewalk and a curb – is something that holds them together: you need to fill, to make it watertight, in order to restore the integrity of the surface and/or structure as a solid, built thing. A crack is something to be fixed.
In landscape terms, it is possible to consider a joint as a space in which something can happen: a dynamic interface between constructed and living systems, between pedestrian and vehicular spaces. Cracks connect things with each other: a crack or joint may allow stormwater to percolate, or plants to grow. In ecology, an ecotone supports greater biodiversity than either of the two areas at its borders. A crack may be seen to have positive value.