One of the problems with 3D printing, especially the Fused Filament Fabrication / Fused Deposition Molding type that is common, is that the parts often display layering, striations, and other artifacts that add up to a lousy surface finish.
However there are now ways around that.
One of the new types of 3D printer filament is carbon fiber. It is either ABS or PLA plastic with chopped very short strand carbon fiber mixed in. The thing is that the carbon fiber does not lend itself to a huge weight reduction nor a large strength gain. Rather it makes printed parts print without the lines and it prevents warping and shrinking.
I suspect that it also will work with the glass filled plastic resins, however I have not had much opportunity to mess with that yet.
Proto-Pasta has a carbon fiber filament that also has a high temperature PLA plastic. It prints at normal temps, however it ca be baked and a chemical reaction occurs that makes it more of a thermo-set with distortion temp going up to 140c. Plenty good enough for automotive parts.
Other times the layers can be desirable. For example, I have a little side project brewing to make some knife blanks. I will also print handles for said blanks from PLA wood filament at a thick layer to give it a nice grip and give a wood grain appearance.
Basically a really nice knife blank from some of the same stuff I made the high dollar knives a few years ago, but instead of using 1/4 inch plate, I'll go down to 1/8 inch, and skip the expensive hand made micarta handles and tripe to the tool and die shop.
Printed wood PLA also makes nice wood grips for various tools, and firearms.