Depending upon your application, the difference between NAD27 and NAD83 may be significant - not so much for most SAR operations, but critical to many archaeological applications.

At least in the lower 48, a lot of the topo maps are in NAD27. It is worthwhile to determine when the data on which the map was produced - maps currently in use for Channel islands National Park are based om aerial photography flown in 1943 (can't imagine why the military was concerned about mapping Pacific coastlines and islands in the early 1940's). the topography is still current, but cultural features - roads, trails, and buildings - are way out of date.

My experience is that trails shown on maps produced before aerial photography came into vogue show trails quite accurately, while those produced from aerial photos frequently mislocate trails.

So, don't just blithely trust the map. There is a lot of pertinent info in the fine print.

I think the bottom line is, work on your navigational skills and use the maps, GPS units, whatever to their full potential. I have taken the coordinates of my vehicle before launching out and I have been glad I did more than once - a worthwhile practice.