I find it seems natural to add as you go along, the totals are easier with only 6 numbers (Hopefully!!) having played a lot of golf it may be a carry over from that.
Also i tend to think along the trend rather than pure score, if im dropping down into say averaging 8 and a bit on a Portsmouth i know something isnt quite right, where as an odd 8/7 creeping in is not too upsetting