Or for other purposes. The following assumes that you have a pencil sketch or so and want to make a t-shirt-able SVG from it. After some amount of probing, the following path^[1] seems to be the most promising for me:

Import the image. Not sure if smooth or just the default auto is better here. Tried both and cannot tell the difference so far.

Add a second layer for tracing and drawing. Trace the image. (Path → Trace Bitmap (Shift-Alt-B)).^[2] For me, the following settings work best: Single scan, centerline tracing (autotrace), smooth corners enabled and set to the maximum.^[3]

Now you have a path with many, but not too many (presumbably because of the high smooth value) nodes.

Right now is a good opportunity to use a different color for the traced path. As you have just one path, change of color affects the whole path when you do this change right now. Of course you can always select all paths and change color, line thickness etc. later.

Using a different color makes it easier to tell apart your path from the scanned image. Blue may be a good choice. I myself don’t do this, when I want to tell scan and path apart, I just make the appropriate layer invisible. But as they say, YMMV.

Next, break the path apart (Shift-Ctrl-K). This step is important. If you keep the whole trace as one path and simplify it, strange things happen. Parts of the path just twitch around. The reason presumably is that a lot more nodes are considered when simplifying, so that nodes that are far away from each other still influence each other. Maybe. Or, maybe not. I’m not enough of a graphics expert to know.

After this, you can either select each subpath and simplify it (Ctrl-L), if it still has to many nodes for your liking. Which it will presumably have, some shapes like the letter "O" can be reduced to a few nodes without problems. And the fewer nodes, the smoother the path becomes.

Alternativly, I tried to import the bitmap and trace it by hand. But that’s a lot of tedious work that you can also leave to the computer. And if you don’t like the result of the tracing, just delete that part and redraw it by hand.