Don't get Gimp and Inkscape confused. Gimp works with bitmaps and inkscape works with vectors. If you don't understand the difference, don't feel bad, a lot of people don't. Think of a bitmap as a grid of squares drawn on paper, you fill in each square wit a color. That's why some graphics have jaggy edges. Bitmaps are like what you get from a camera or scanner. Like a photo, they can and usually have several colors and are complex. The problem is that if you try to scale them up or down too much they fall apart. That's their big downfall, they also have really big file sizes.
NOW, consider a vector as a piece of paper with mathematical instructions on it telling us to 'draw a line from this point to that point', simple. You can scale a vector up or down almost infinitely. Vectors usually have less colors and smaller file sizes. If you make graphics it's good to have them both. if all you do is edit photos you don't need a vector program. Personally, I can't get by without having both, they each have their uses, strengths and weaknesses.

I mostly use inkscape when I want to draw paths freehand. I then import the paths to gimp and colour/stroke them with gimp.

I really like inkscape's freehand path tool, it's something that I wish I could do directly in gimp... yes, there's the selection to path tool but it's not the same - only works for closed paths and is way less accurate.

very nice job of that bottle Rod.
I don't use Inkscape. I find it difficult to learn and I have enough on my plate just to learn Gimp, and all the new scripts etc. I am not what a person would call a multi-tasker lol.