It depends. Resurfacing is only helpful when rotor wear was uneven.

Rotor will wear out faster. Some shops recommend changing
rotors to avoid paying twice for pad and rotors replacement.  

WRX, I assume, has disc brakes on all four wheels and a four
wheel drive. So the wear will be about even - particularly on
manual models. With FWD, most of the brakign job done by front
anyway.

DK

Hi,

As Carl said, you need to take a little extra time and care "breaking"
in the new pads to the old rotors. Once they're worn in, stopping will
be fine, though perhaps a bit noisier than with perfectly smooth rotors.

For myself, I've never resurfaced rotors on my own cars. Doing brakes
for others, yeah. Most shops want to do it cuz of the liability issue as
well as the extra income. If new pads are placed against smooth rotor
faces, they don't have to worry that Joe Customer's headed down the
street w/ only about half the breaking he expects for the first few
miles.

Ceramic pads? One of my clients was a brake mechanic for a large
dealership until he retired this year. He said ceramics were going to
"put him out of business." They wear longer than other pads, and don't
cause much rotor wear. Only caveat I've seen w/ ceramics is to do the
conversion w/ NEW rotors (check w/ the mfr to see if they have "ceramic
specific" rotors in their catalogs--some have varying grades of
replacement parts, and match the cheapest pads with the "factory warped"
Chinese rotors, the better pads w/ the straight Chinese rotors, the best
pads with... well, you see the progression.) I haven't heard the noise
or seen the dust issues w/ ceramics that were mentioned in another post.

Good luck whichever way you go!

Rick

Rick and Carl had the most common sense responses, IMO.

Since rotors are usually made of cast iron, the material varies in hardness and
different parts will groove under the same force. So the decision to replace them to
get a smooth surface is a very short lived gain.

I would like to see a study of the change of rotor thickness while the pads
are showing little wear.

Peter's question references the non-existent rule book of auto repairs.

Pads are pads, and rotors are rotors. For the most part, organic pads are cheapest,
metalic more expensive, ceramic usually most expensive.

Why? The act of braking is the act of converting the motion of the car into heat.
That's it! Therefore, you want materials that transfer heat away from the brake parts
as fast as possible. Organic, slowest, metalic, better (metal transfers heat better
than organic stuff), and ceramic, well, I haven't seen enough info yet since ceramic
material is an insulator (the space shuttle uses ceramic tiles to protect during
Earth re-entry).

Rotors are more difficult to rate because every company out there gets their
rotors from a different manufacturer, on each shippment, so it would seem.

Unfortunately, you can't even rely on buying "ACME PRIME GRADE" rotors
from "ED's Auto Parts" twice in a row and getting the same thing, since Ed's
auto parts upline distributor's supply constantly changes.

In other words, you have to rely on your auto parts place to have the integrity
to check their suppliers who change constantly up the supply line somewhere.

Avoid those damn Chinese rotors. They're cheap, but not machined straight.

What to replace depends on just plain old mechanics, just like Rick and Carl
were saying. Replace pads when required, replace rotors when required.

Brakes work remarkably well even when things are not perfect. That's a good thing.
A few miles after you put all new parts on your brakes, they will be wavy, unevenly
worn, dusty, and subject to all kinds of contamination from the road and environment.

Therefore, there is some play room between when deciding to replace, turn or maybe
just break the glaze off used rotors when changing pads. Leave the decision to a
good mechanic who has all the facts.

However, anyone who wants to create a rule like "always replace rotors" either
knows something unique about a particular model of car, or just wants an easier,
faster brake job for HIM to make more money. There is no universal rule.

The Ole Factory Rep (not Subaru)

I never worried about gruves. Till the pads make full contact, the car
won't stop as fast, but then you have more contact area when they do.)

VF

On my 2003 XS, I just replaced pads on all 4 wheels for the first time
at 71,000 miles - so obviously I'm not hard on brakes.  I  used stock
pads and  I didn't do anything with the rotors.
   Brakes work fine and back to original in every way.