I have used TSP for many years to remove old grease and grime from old varnished wood. However, as others have pointed out, you won't want to use TSP unless you are committed to revarnishing what you have cleaned. I have also used TSP on painted surfaces, but beware, you don't need much elbow grease or water. Just a damp rag soaked in TSP solution (based on measurements on package) and wrung out well. Too much scrubbing may remove some of the old paint.

TSP is used as a de-glosser before repainting or refinishing old varnish/urethane, etc. I am getting ready to put a new finish on my tired knotty pine. Fortunately, mine is gorgeous except the finish has dulled over time. I am going to clean with TSP and then add a new coat of Urethane.

Hope this helps.