Cropping to reduce FoV of wide angle lenses

Oft quoted are the benefits of cropping a FF sensor with say a 300 mm lens to improve the 'reach' to around 450mm (DX)

On a similar tack, what would be the effects of cropping a wide angle lens to achive a slighly limited FoV? In other words, would it be better to buy an expensive wide angle, say 20/21 mm and then crop to achieve say 24mm or to buy both 20/21 and 24mm lenses at a total cost equivalent to that of the more expensive wide angle lens?

DoF would change (using 2 lenses) but is this a 'good thing' or a 'bad thing'? What are the other positives and negatives of cropping a wide angle used for different ends of the spectrum, reportage and landscape?

Interested in your views, particularly those that have tried this approach, to make a 'zoom' out of a fixed W/A lens now that there are high MP cameras available and cropping won't degrade the resulting image too much (at least when compared to the earlier generation cameras).

Food for thought?

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AJ
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