Depends on your tank. Skimmers are unmatched in terms of their ability to remove wastes from the water column before it becomes part of the metabolic processes of reef. If you want to have any sort of success with things like SPS and/or NPS corals, you WILL need a protein skimmer. If you're only keeping things like mushrooms and Xenia, this becomes less of an issue.
The whole nutrient depletion issue is a myth, IMO. Calcium does not bind to the foam substrate produced by a protein skimmer and any other elemental stripping (being mostly negligible in nature) can be compensated for via feeding/waterchanges/additives.
Overall, I would readily recommend that all newbies invest in a skimmer. They provide a much needed buffer zone against common mistakes like overfeeding, neglecting a water change over a weekend and the like.
HTH's.