A woodworker can never have enough clamps. It doesn't matter whether they're bar clamps, pipe clamps, quick clamps or spring clamps, at one point or another, you'll likely wish you had more clamps. Even though it's one of the cheapest clamps to purchase, the basic spring clamp is absolutely invaluable in the wood shop. They're strong, easy to position with one hand, and with their relatively low cost, it's easy to have dozens in your shop.
Spring clamps can range in size from quite small to a standard, relatively strong woodworking spring clamp that is about the size of the clamp on a pair of battery cables. Spring clamps are rated by the size of the opening - a spring clamp about the size of a battery cable clamp would probably be a 2" spring clamp. This is the only size that I use in my wood shop, as smaller clamps rarely are strong enough to hold pieces in place.
When you look for spring clamps, be sure to get those that are designed for woodworking. That is to say, they should have a strong spring, but one that isn't so strong that it can't be attached with one hand or that it crushes the wood fibers of the stock. Additionally, make sure that the tips of the clamp jaws are covered with a protective plastic or rubber-like cover that will not mark or mar the surface of the stock.
A spring clamp can be used for numerous tasks around the wood shop. For instance, in the picture above, I'm using spring clamps to hold a Band Saw Circle Cutting Jig in place on the under side of the band saw table. Notice that it takes more than one clamp to hold the jig (in my case, I use four spring clamps to hold the jig steady).
Spring clamps are also terrific for clamping glue-ups, or holding molding as it is being nailed in place. However, be aware that spring clamps tend to allow a piece to slide a bit as the pressure on both jaws of the clamp equalizes. Adjusting the clamp slightly will often solve the problem. Until you get a handle on how to prevent the problem, always check the positioning of your stock to make sure that it didn't "walk" slightly before nailing it in place.
TIP: Spring clips should be avoided when clamps are needed for safety purposes. For instance, I would never rely on a spring clamp for holding a featherboard in place, as a spring clamp can easily be moved or pushed out of place (where a bar clamp or quick clamp will be less likely to move).