If you ever tried a window manager that doesn't use overlapping windows, you will have found that some programs create too many windows to work well with it. You can let these programs use an X server that displays in a window of your first X server.
Note: this trick is useless if you want to make a vector drawing. If you're using inkscape for something that should eventually become a .png or .jpg or .gif or etc etc, then it might be useful.
When drawing really complex shapes (such as long texts on paths), inkscape can become very slow and may even crash. You can work around this by isolating the complex shape into a separate drawing. Make sure that drawing has a transparent background (file - document properties - page - backround should show a block pattern on the left and a solid color (usually white) on the right)). Export it at the same resolution as you want to export your final drawing (or maybe the double resolution is better, especially if you want to export at a lower but higher than half resolution too). Delete the complex shape from your original drawing, and import the .png you just exported to replace it.