Just so you know… buying the set all at once is cheaper than doing it piece by piece, but the set is a great idea to see how you like them before you invest.
A 24" is great for larger things like scarves in the round. It really depends on how many stitches you’ve cast on and the weight of the yarn you’re using. If you use fingering weight and want to cast on 30 stitches… no way it would work except as modified ML. :teehee:
Jan is right, it is less expensive to buy the full set of whatever tip style you like all at once. But you can certainly expand as it works best for you. Sometimes a piece or two at a time is the best/only way to proceed. The try it set is just the least expensive way to find out if you prefer wood, metal or plastic tips for your interchangeables. And it’s nice to have a couple of spare tips around. There’s no such thing as too many needles! 
However you acquire your full set, you’ll absolutely add to it over time, longer cables, size 13+ tips, etc. Interchangeables make knitting so much more practical. Instead of cluttering my home with oodles of fixed circs in every conceivable size, I just clutter one drawer with 3 pair cables, and oodles of tips. In a tiny home like mine that’s perfect: more space for yarn!
You may find that you wouldn’t use the very small and/or the very larger needles of a full set anyway. So with the starter set, you get some middle sizes and can add whichever tips you need and not have some in sizes you’ll never use.
I already ordered the Try-It set this morning! So much for waiting until after my trip. Lol. I figured since the Try-It set is so much cheaper, what the heck, right? Plus I really want to try the 3 types of needles (even though I’ll probably end up settling on the acrylics anyway), and like suzeeq said, I really doubt I’ll be using the really small needles much anyway. Plus I’ve recently discovered that I LOVE working on size 13 needles, and I plan on making bulky cowls and whatnot in the future, so I didn’t like that the big set didn’t have any 13s. I figured I might as well just start small and add to it slowly as I go along. I can’t WAIT to get my needles!! :woot:
Way to go! :happydance:
Amen Sister! Do what works best for you!:woot:
:yay:
Knitpicks interchangeables are so versatile. They have a connector that connects two or more cables so you can make it as long as you want. I can leave my work on the cable, disconnect the tips, connect them to another cable and use them for something else. They’re also great to keep reserve stitches live, like when I’m knitting glove fingers.
I thought the set was expensive at first. But when I thought of the hundreds of dollars I could spend buying straights, circulars, and double points in the various sizes and lengths, the set was a bargain. And think of it as a one time investment that you will use for years to come. Aren’t you worth it? lol
http://www.knitpicks.com/cfaccessories/accessory_display.cfm?ID=80637
That is SO cool!! I should be getting my set on the 13th! I’m so excited!
And think of it as a one time investment that you will use for years to come. Aren’t you worth it? lol
They should make a slogan that says, “KnitPicks interchangeable needles… because you’re worth it!” 
ETA: I just found this package on my doorstep!!!
I thought maybe my needles had gotten here in ONE DAY, but the kicker is, they’re addressed to my boyfriend!!! I showed him the link to the needle set the other day and told him how badly I wanted them, and it looks like he may have gotten them for me! I’m DYING to open it, but he’s not home from work yet! Oh man, do I love him to pieces! It sucks that I ruined a surprise for myself though! BUT YAYYY!!! :woot: