Not withstanding excellent advice above, in my experience the need (or even advisability) to etch depends on at least two factors.
The first is the condition of the ribs. Etching solutions, to the best of my knowledge, are all extremely corrosive and really shouldn't be put anywhere near a loose rib as they will tend to get underneath it and start all sorts of horrors in that lovely dark, often warm and inaccessible place! This is especially the case where the etching involves laying the barrels in an etching solution.
The second is the nature of the damascus. Many damascus tubes have what I would describe as less metallurgical difference between the iron and steel than others. Browning these without etching can be a laborious process as they lack the dramatic difference between the brown and silver that everybody yearns for nowadays.
However, some tubes have a startling natural differential between the iron and steel and need the lightest re-brown to achieve a very fine finish.
I am browning 3 sets of tubes as I write: a set by a small London name that I am struggling to get much contrast on; a set of Boss tubes that have a wonderfully fine pattern which have naturally etched a little over the last 140 years and should show a good contrast when finished and finally a set by Blanch that pretty much browned themselves with only a light rub over with 800 W&D and about 8 passes of a very mild browning solution, giving a high contrast silver steel and crisp brown iron.
If you are going to brown them anyway, I suggest you try a light, but thorough, rub down with 800 W&D and a few passes with your favourite browning solution before you start etching them.
You can always etch them if that is not getting you the finish you want.
