This has been posted several times. There are those that say it isn't necessary and some, me included, say you should 'break in' a new barrel/rifle. There are different methods including the clean after each shot for the first 10 rounds, then after each 3 shots for the next 30 or so. Now for the why. Most people believe that this is done to improve accuracy. Not true - at least not immediately. The purpose of breaking in is to remove the minute burrs in the rifling and allow for easier cleaning in the future due to less fouling accumulation. That is where the accuracy factor comes in. After years of shooting (normal shooter shooting a box of ammo a year), even after cleaning after each session, fouling can build up which can deteriorate accuracy. This would be especially true for those old timers who think that running a patch of Hoppes #9, a couple dry patches and then an oiled patch down the bore is all that is required to clean it.
So its your investment - if you don't want to go through the trouble of breaking in your new barrel so be it. IMO the hassle in the beginning is worth it in the long run.