Yes, but only up to a point.
My three finger-joint boxes/drawers are made using red oak as this is my wife’s favorite, plus matches the cabinet where they will go, and with only a couple of exceptions I finish that wood with Watco (usually followed by a couple coats of paste wax). So after all of my pieces were completed I decided to finish them (sans the wax since these pieces will see some heavy use and am planning on putting on a couple coats of polyurethane) to avoid having to do it later since doing the insides, along with the bottoms, would be a little more difficult after assembly.
Just as an aside I did not realize how tedious getting these pieces ready to finish would be since I needed to tape over all the flat glue surfaces of the finger joints first. Additionally decided to put tape over the portion of the wood below the groove for the bottoms for a really neat tip I had read. Since plywood is almost always thinner than router bit diameters, or dado blades, this leaves the bottom loose. To keep the bottoms tight, glue some small blocks onto that small section below the groove pressed up against the bottom.
So two coats of Watco and some more tape in the inside corners to catch any glue squeeze out and assembly commenced.
With my boxes being assembled today was the day I decided to plane the finger joints flush with the sides. I had left them about 1/32″ proud based on most of the articles I have read about cutting finger joints.
Though before I started doing that I made this jig: http://www.finewoodworking.com/FWNPDFfree/jigs-for-planing.pdf, except I only made the larger part since I do not have a tail vise like shown in the article, cutting slots to fit my two drawer dimensions. I clamped the jig to my workbench and put one of the drawers on it, using a softwood wedge in the slot to keep the drawer from moving, and began planing using my Lee Valley low- angle block plane with their optional knob and tote (this turns that block plane into a small bench plane).
Admittedly I am not the absolute best at using a hand plane, but am trying to improve. I set my plane for as fine a cut as I could while still making decent progress with each cut, but found I also cut into my sides as well when getting down almost even with the sides, though not everywhere – so there went my finish efforts on the outsides.
This was also my first time to use, and appreciate a scraper using it to remove the plane blade gouges. Sanding and two more coats of Watco followed.
Should have stopped to realize that putting finish on the outsides would not be difficult, I was just trying to “use my time and materials effectively” – lesson learned.
So yes do pre-finish but not on any surfaces which you have to work on, or next to, that might be “in harm’s way”; unless you like to re-do previous work or just want some more practice.
Oh yes, this afternoon my beautiful wife informed me she wants me to make two more of these drawers – good thing I’ve had plenty of experince!