If you're reprojecting your map and using a more local area (say, just one continent or country), then you will definitely need a different guide. The notion of a "scale bar" isn't generally meaningful for most projections that are showing large amounts of your world because the scale varies from place to place, depending on the projection ( see https://en.wikipedia.org/wiki/Tissot%27s_indicatrix for a common tool used to show variance in distance and direction in different places on a projection).

Another common decoration on maps is a wind rose (that thing that points at north). Just as "scale bar" doesn't mean much for many kinds of map projections, a wind rose isn't particularly meaningful for most projections as well. A wind rose can indicate the direction of North from the point where it's sitting, but moving it around will likely require that it twist to find the proper direction (quite difficult on the printed page).