If you want to remove an old finish in order to put on a new one, it’s almost always better to strip the finish than to sand it off.
First, except in cases where the old finish is flaking off, it’s a lot more work to sand than to strip using a paint-and-varnish remover. But more importantly, sanding cuts through stain and “patina” (the color changes in wood caused by light and oxidation), and it does so unevenly. Once you start cutting through this coloring, you have to sand through it everywhere to get an even coloring for refinishing.
Stripping is messy, which is probably the reason many people chose to sand instead. But stripping is usually a lot less work, especially if you can be patient enough to give the stripper time to dissolve through to the wood. The overwhelming percentage of old finishes are either shellac or lacquer, and they dissolve and liquefy. All you have to do to remove the sludge is scrape or wipe it off.