Hi AeroSpark,
Yep, a Monitored Approach is a fairly common procedure. The procedures vary between operators, so you won't find a specific answer that applies to the whole industry. For example, I've worked with a company whose procedures for a monitored approach had the First Officer fly the approach and the Captain took over only for the landing. At another shop, we permitted a "Reverse-Monitor" where the FO would conduct the landing and the Captain would monitor. At my current gig, the Captain flies all monitored approaches.
The advantage of a monitored approach is that instead of both pilots being "heads down" until minimums, the Captain will begin looking outside about 100 feet above the minimum altitude. This permits the Captain to become accustomed to the outside environment to conduct the visual landing. For example, illusions such as wind drift or blown precipitation could cause the crew to conduct a missed approach were they to look up right at minimums. It also ensures that the First Officer remains on the instruments through to the landing roll to identify and call any deviations which may otherwise be imperceptible to the Captain. This differs from a "non-monitored approach" where as soon as the pilot flying calls "visual" or "landing" the pilot monitoring can look outside as a part of their scan.
At my company, we are required to do a Monitored Approach for:
1) any CAT I precision or Non-Precision Approach where the reported visibility is below the advisory visibility (remember that cloud base is the determining minimum for an approach, not the visibility), and
2) all CAT II and CAT III approaches.
I think in a year I might fly five monitored approaches, and often most of those happen on the same day, so it's not necessarily common for an individual to conduct a monitored approach, but they certainly happen every day around the globe.