Use of Closeup filters

I just picked up Canon 52mm ProMaster closeup filters +1, +2, +4, all this for $5 from a garage sale.
To try, I decided to take few images with each +1, +2, +4 for roses.

Attached are some images, all in M Mode taken with D3100 + 18-55mm VR.

I did not find any big difference with using the 52mm closeup filters. If no filter would have been applied, the images could have been similar with the regular 18-55mm VR lens.

My question to my friends and all experts is: what is the use of closeup filters +1, +2, +4? How and when to use them?

Images Crop and PP in Windows Live Photo Gallery.