as a separate application or do you find Gimp enough?

Strangely enough I keep downloading updates but never use it. I might have a go one day but I find Gimp does most things I want graphics software for.

But they have different uses. Bitmap and vectors.
I use Inkscape in a very basic way. To make some logos or icons. Things do not lose resolution when resized.

I don't use it a lot but it's a good tool to have handy.
Along with what's already mentioned, Scalable Vector Graphics (SVG), wire-framing, maps...

I used to design an entire company's handouts and folders for multiple banquets and conferences.

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 always download but i never used (in years i would have opened 3 or 4 times )

I found so unintuitive vector graphic programs, so i never use, but i always plan to start using

Vectors have to be treated and seen differently than bitmaps. I started using Xara 5 and even though it was expensive I use inkscape more. There are things one ca do much better with vectors than bitmaps.

Yes and in combination they make a suite that is very good in terms of graphic design for the open source junkies such as me

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.