We have struts, trucks and some other cars has shocks. Struts allow/bring the wheel back to postition after something has changed it course. I.E. if you hit a pothole, speed bump, that sort of thing. It's alost assists in hold it in place when cornering and in driving in general. If it were up to just the spring alone we'd all bounce down the road.
If you have the money get coilovers. I highly suggest function and form vs 1's. You can get them on ebay for around $630 shipped. (well used to be able to. I just checked and they're not listed right now).
How many miles are on your stock struts? If they have too many miles (75k or more) they won't last long once you put on lowering springs. If you lower less than 2 inches you should be good for 50k miles or more on new struts. The lower you go, the less life you'll get out of your struts.
Think of it this way. You'll pay $100-$200 for springs. If/when you buy new struts they cost $220 ( I just bought KYB GR2's for $220 shipped). So you have $300-$400+ in parts. If you keep it long enough you'll have to replace the struts, spending another $200+. So you're at the cost of coilovers. The struts that come with coilovers are designed to be lowered so they should/will last longer than an OEM style strut. So you can spend the money and "do it right" the first time or just buy springs and replace the struts as needed.