Springs/Coilcovers vs Springs

Can somebody help me with this issue. I've searched already in the suspension section but still not really sure how this works... 
When lowering a car ex: your MB w203, Why would I want to go with springs with coilcovers vs just springs? What is the difference? If someone can explain and help me understand I would appreciate it.
SECOND: I went to the Euro Car show in SD yesterday... and I would just like to tell every member on this forum (YOU KNOW WHO YOU ARE THAT WENT) I was amazed at how beautiful all your cars looked! WOW
never been to a Euro car show and I cant wait till the next!!! Keep up the awesome work. I didn't say hello to anyone... my car is stock so I just didn't feel worthy
but managed to snap off multiple shots of all your cars!!! BEAUTIFUL!

Can somebody help me with this issue. I've searched already in the suspension section but still not really sure how this works... 
When lowering a car ex: your MB w203, Why would I want to go with springs with coilcovers vs just springs? What is the difference? If someone can explain and help me understand I would appreciate it.
SECOND: I went to the Euro Car show in SD yesterday... and I would just like to tell every member on this forum (YOU KNOW WHO YOU ARE THAT WENT) I was amazed at how beautiful all your cars looked! WOW
never been to a Euro car show and I cant wait till the next!!! Keep up the awesome work. I didn't say hello to anyone... my car is stock so I just didn't feel worthy
but managed to snap off multiple shots of all your cars!!! BEAUTIFUL!

