Use the right tool for the right job!
Thicknessing guitar tops and backs and sides by hand, with a hand plane is fine if you only make a handful of guitars a year. But if you make quite a few, as I do, thickness sanding is the way many go. A lot of shops invest in a small drum sander to thickness tops. Like a Jet drum sander or a Performax. I did the same once. Used it once, and sold it! They’re crap. Truly underpowered for the job. I much prefer using large machines for this job. So what I do is seek out a local cabinet making shop, and hire their big machine for a couple of hours every few months. You get a much better result this way and it’s a lot less hassle. And cheaper too.
But even then there is a skill to using these machines. Watch out using hard exotic woods like rosewoods. If the dust extraction is too strong it can lift the wood up into the rollers when sanding with a fine grit which burnishes the surface and makes it slippy. I know, I learned the expensive way!