If you plan to sculpt in mudbox or modo 501 it would be a good idea to UV before sculpting that way if you want to do any texture painting on the high resolution mesh it won't be a problem.
UVing a high resolution mesh is generally pretty difficult...
Whatever you feel most comfortable. I won't be the first to tell you this but everything can be done a million ways in this industry.
If you're going to bring the model to zbrush or mudbox, depending on what it is that your making / what you want to make, you don't need to do uv's right away.
A more common workflow, it seems nowadays, is to build a base mesh in maya / max etc to fit your concept or idea well enough to take into zbrush / mudbox and start sculpting on it. Once you are done sculpting completely, you can just retopologize that HP model and uv THAT. If you're gonna paint your model completely in zbrush, i'd just use the uv tiling processes in zbrush itself to handle the uv's, and then just paint away.
In Zbrush with GoZ you can always send your mesh back to your 3D app and unfold it there, or even use the UV Master tools to unfold it right in Zbrush when you need to.
As many people said, yes having UVs on your low can be useful for quite a few things, but not really necessary.
As far as zbrush goes, I'd say to save the final UVs for the end. I would think this way the final UVs would better match the final mesh? If you do want some UVs for the sake of polygroups, a quick temporary UV set will work just the same. Select an arm or whatever, give it a random subprojection, then collapse into a single point. It's a much quicker process, and just as suited for creating polygroups.
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UVing a high resolution mesh is generally pretty difficult...
Whatever you feel most comfortable. I won't be the first to tell you this but everything can be done a million ways in this industry.
If you're going to bring the model to zbrush or mudbox, depending on what it is that your making / what you want to make, you don't need to do uv's right away.
A more common workflow, it seems nowadays, is to build a base mesh in maya / max etc to fit your concept or idea well enough to take into zbrush / mudbox and start sculpting on it. Once you are done sculpting completely, you can just retopologize that HP model and uv THAT. If you're gonna paint your model completely in zbrush, i'd just use the uv tiling processes in zbrush itself to handle the uv's, and then just paint away.
As many people said, yes having UVs on your low can be useful for quite a few things, but not really necessary.