My rationale is two-fold:
1) Since most patterns are multi-sized I've preserved the pattern for use in another size thereby avoiding the cost of an additional pattern
2) In the event of fitting (or other) mishaps I can refer back to the unscathed original
Since my basement studio has less-than-stellar lighting, tracing is sometimes cumbersome and it is easy to miss small details like notches and other markings, especially on BurdaStyle Magazine patterns.
A typical BurdaStyle Magazine Pattern Page
I've always traced with a bottom-up approach by placing my new paper on top of the pattern and tracing the lines that show through from underneath. I'm not sure why other than it never occurred to me to approach the task differently.
If the original pattern is printed with dark lines on heavy white paper (such as vintage Kwik Sew and a number of independent pattern designers) tracing is simple.
Tracing a pattern piece from Angela Wolf's Ruched T AW1123
However, attempt this with a multi-piece Cutting Line Designs pattern (or even worse BurdaStyle pattern) and one is tempted to say forget it, just buy another pattern. While the option to purchase another pattern is there, it is not always feasible. (As in an out-of-print pattern.)
But alas! There is a much simpler top-down approach that will require a short trip to the office supply store for carbon paper. Yes, the stuff that, if you are old enough to remember, used to be rolled into your Remington.
Yes, they still sell this stuff.
Get your tissue pattern piece ready by pressing with a dry iron on wool setting. It's very important to remove all the wrinkles unlike mine in the picture which could use a bit more pressing.
Getting the piece ready for the Two x Four Pattern
by Cutting Line Designs
Set the pattern piece aside and lay out the blank tracing paper first followed by a layer of carbon paper sheets. Because the multi-pack contains many sheets I can cover my entire area.
Now, lay the pattern piece on top using weights to hold it in place. This creates a sandwich with blank paper on bottom, carbon in the middle and tissue on top with right side up.
Simply trace along all the lines and markings from the top using your rotary marking wheel.
Voila! Once done, the dotted lines are your pattern traced onto a separate sheet of paper leaving the original pattern is unscathed.
To be more efficient use a double tracing wheel and mark stitching lines at the same time but make sure it is set for the correct seam allowances.