The ideal spot for a rock shelter. South facing, with the ridge as a great barrier to the north winds, with a nice platform to lean logs against the cliff, could have made this a des-res in the days when rockshelters were the height of fashion. It's also got the obligatory excellent views of Cheviot and I think it would have been intervisible with the goings on at Roughting Linn. Though the carving of the outcrop at Roughting Linn most likely occurred a good while after Goatscrag was being used, there's a strong chance that the Roughting Linn outcrop had significance for long before it was chosen as a rock that needed to be marked with cups and rings.
One other interesting feature of the outcrop is the way that the dep fissures which are home to nesting birds channels the sound of hungry chicks, so that you can stand in one spot, moving your head from side to side, and whilst leaning left, silence, then when leaning to the right, loud chirruping. It gave me quite a start when walking past, there was a sudden blast of noise that vanished in a second. It probably hints at this having once been a good spot to go hunting for extra protein in the form of hidden eggy comestibles.
The deer carvings are so basic, and so anomalous. there have been doubts about their antiquity, but the crudity, and the definite weathering do give them a high likelihood of ancientness. Their anomalous nature, being one of the rare examples of representative rock carvings in not just Northumberland (where they are the only example of such), but in Britain and Ireland also, makes this a significant place. It's possible that the orientation of the cliff face which makes it so sheltered, it the reason why the carvings may have survived. it's equally possible that other similar surfaces once bore similar marks, but that the more exposed surfaces have long since been sandblasted by the elements, so that no trace of carvings remains. There are a few patches on the vertical surfaces of the Bowden Doors that would be good candidates for such unprovable claims.
Another thing that makes me lean towards the idea of the Goatscrag deer being prehistoric is the nature of the more standard abstract carvings on the outcrop above the shelter. The small cups with their horseshoe linking arcs remind me of Australian Aborigine motifs which are said to represent humans sitting in camps. It's a highly tenuous link, and it's supposed to be bad form to make anthropological comparison across space and time (for many good reasons), but hey, the pondering of improbables is a large part of the fun of going to look at ancient carvings.