It depends on your definition of "worth".
I recently pulled all my investment sets except one off the shelf so I can part them out, because the additional work turns out to be financially worth it to me at this point in time.
If I weren't already working full time as a seller online and had other employment, holding longer term for investment, or flipping sets for a small profit, might be more attractive to me. Since I don't, I've found parting out Lego to be a fine addition to our business and cash flow, allowing me to get my money and more back out of each set faster and put it into the next round of sets to part out, lather, rinse, repeat; while still retaining a healthy portion of each set in inventory that turns more slowly (but increasingly steadily) allowing me to increase our inventory faster and actually pull a profit from this after only a very short time in Lego.
For those who don't want to put in the additional time on such a project, for those who loathe that particular type of work, for those who are not organized enough to deal with a parts business, for those who can jump start their Lego cash flow with quick flipping of discount/in demand sets and/or don't need money back from their investment for a few years, buying and holding sets is sometimes the better option.
But don't poo poo parting out. There's money to be made in it, if that's the way a given person wants to make it.