I’ve found that reading up on your favorite lenses is not as fascinating as listening to professional photographers talk about them. If you’re just upgrading to a dSLR, you’ll quickly learn that lens choice is not only about the expense but it’s more a question of what style you’re going for in order to justify the purchase of more. From my own experience, I think it all depends on a couple things. 1) Where do you shoot, 2) What do you shot and 3) What look you’re going for.
Without question, professional photographers can easily outspend their cost of equipment by acquiring any lens they want but I’m sure their decision on any new glass is dependent on how instrumental it will be to their work. It’s easy to get confused about which lens you’ll need so that’s why I’ve found it helpful seeing these videos of professionals list the lenses they require for what they do rather than admitting it’s equipment they just wanted.
Granted they’re speaking specifically about Nikkor Lenses but the focal lengths mentioned can be applied to any brand that offers them: