Yes, a landmine ban would benefit small countries as small countries tend to be the ones at greatest danger for unexploded landmines. If landmines are taken away as a tool of war from both sides of a conflict, then the small nations which most often use those mines would not have the issue of unexploded mines in their territories.
Like nuclear weapons, landmines offer nothing but death and destruction. No countries need to harbor landmines if at all possible and a landmine benefit would benefit any country, small to large. Landmine bans would help prevent the injuries and deaths of many people, including unsuspecting children who stumble upon them.