Originally Posted by Wilfred Laurier

The main things that will need adjustment are (1) the shifting (the cable housing will compress slightly and this has the safe effect as the cable 'stretching', which will throw off the shift indexing), (2) Bearings may need adjustment to remove play that developed during break-in (if there is any rattling coming from your wheels or headset then you should have the shop should take care of that immediately); (3) t6he machine built wheels will likely require their spokes to be retensioned after a few hundred kms (letting the spokes stay loose after break-in will result in an out-of-true wheel or broken spokes).

Another thing to keep in mind is that many bike shops will do minor adjustments and not count it as the 'free tune-up' - if something seems like it is not working 100% (for instance, gears don't shift smoothly with every 'click' of the shifter"), the shop may be able to quickly fix that one problem and get you quickly back out on the road, then lay down another few hundred kms and take the bike back before you put it away for the season.

Also, as others said, many of the things they do for a 'tune-up' are quite simple, and if you have even a minor amount of mechanical aptitude and an internet connection you can easily figure out how to do them yourself. This can also come in handy when things go wrong while you are riding and there is not a bike shop handy.