My understanding is that pinhole leaks in copper piping are the result of local water conditions.

The best thing for the OP to do is to phone around to his local plumbers and see whether they find an excessive number of pinhole leaks in copper in that area.

In my case, I had one pin hole leak about 35 years after the building was built, in 1995, and none since.

Embedding copper piping in concrete is supposed to cause pinhole leaks, and in my case, the pin hole leak was in a pipe that had concrete poured around it. Still, the pin hole didn't occur in the portion of the pipe surrounded by concrete, but in a spot an inch or two above the concrete. And, so far at least, the other hot and cold water pipes that had concrete poured around them haven't leaked.

So, I think it's all dependant on your local water conditions. ONE pinhole leak is not justification for replumbing your house cuz you're scared that next year there'll be a gazillion of them.

The only other leaks in copper pipes I've had have been bad solder joints, some of which only started leaking decades after the building was built. Normally, if a solder joint doesn't leak in the first few seconds after water pressure is applied, it won't leak for centuries. But, there's always the exception to every rule, and I've been unlucky enough to have experienced a few of those exceptions first hand.

Bob[44]:
The reason they tell you to clean up any flux residue after soldering is because flux contains a chemical called zinc chloride. Zinc chloride acts as an acid at soldering temperatures in that it dissolves any copper oxide that wasn't removed by sanding or brushing before fluxing. Zinc Chloride attackes copper oxide much more aggressively than it attacks the copper metal itself. But, it's important to note that zinc chloride's acidity only occurs at soldering temperatures. At room temperatures, zinc chloride has virtually no acidity at all, which is why you often see "acid based" soldering fluxes being sold in metal containers. If the zinc chloride was even mildly acidic at room temperatures, a metal container would corrode and be inappropriate to store that flux in. Ya gotta remember that for some DIY'ers, a 2 oz tin of paste flux is a "life time supply". Even residual flux left on the hot water supply piping is of little concern because the 140 degree F temperature that hot water supply piping might operate at is cool compared to the 300 degree F soldering temperatures that zinc chloride operates at. The only time I'd be a bit concerned about residual flux causing any damage is when we're talking about copper piping used in hot water heating systems that operate at closer to 200 degrees F, and even then the zinc chloride isn't going to do any serious damage to the copper. It'll to attack the copper until it's spent, and that will be the end of it's detrimental effect on the copper.

So, officially, you're supposed to clean off any flux residue after soldering so that the residual flux doesn't attack the copper. Unofficially, that residual flux is never going to do any real harm, not even to copper pipes in hot water heating systems.