The bloke in the LBS is not necessarily talking shite IMHO. Contrary to Banjo's humble opinion. The truth is that both are as good as the other with pros and cons either way. The crucial factor for us older types (I am 52) is the low gearing - the high gears matter not a whit for us really - unless you regularly top 40-45mph. I have a triple with a 30 small chainring on the front and a 25 large cog on the rear which gives me a low enough gear living in hilly Scotland. I hardly ever need to use the lowest gear, not because I am fit, but because, frankly it is so low it doesn't come into play particularly often. A typical compact set up has a 34 small chainring on the front and if fitted with a large of cog of 28 on the rear gives a virtually identical low gear to my setup. So IMHO a compact can give you low enough gearing for most of whatever you need.
The advantages of compact is simplicity - both in the shifting itself and the mechanism within the shifter, there is less stress on the chain because the chain runs on a better line and there is a nice spread of gears without much overlap or duplication of the gears and the setup is lighter. The disadvantage is that there is a big drop in gears when you move from large chainring to small, from 50 to 34 teeth and you may have to upshift a couple of gears to compensate. The major advantage of the triple is that you don't have such a drop between the 52/42/34 chainrings, so the gearing is closer together allowing you to maintain cadence.
Some people prefer the compact, some prefer the triple. I have a triple but given an absolute choice would prefer a compact, purely for the simplicity. A triple can be a helluva faff at times.
Well spotted that man, now corrected.
