Refer CMM for formal description, Iíll provide my informal understanding. Itís when you collect statistics of some process with goal to evaluate (and improve) the process. Benefit is that without understanding the details you still have a way to evaluate/improve the process.
P.S. Few out of the list of drawbacks are their blindness to complex issues and possibility to improve metrics without actual improving process (cheating metrics).
?:the art of a constructive conflict perceived as a destructive diagnose.
At maturity level 2, measurement and analysis is about gathering measures for what you need in your business case (e.g. to monitor your project). What do you want to know about your project? Don't gather measures you'll not use! Be sure you know why you gather these measures!
At maturity level 3, CMMI expects metrics. What this mean is that in addition to measures, there are thresholds defined. This should help the projects see if they have to pay special attention to some events.
At maturity level 4, statistics are introduced. The measures/metrics have a certain baseline, and there is a deviation that is known. There are always deviations: some are normal because of the way the solution is designed. These are called "common causes". Others are not normal, but a special event happened. These are called "special causes". At maturity level 4 the goal is to try to minimize, or take action on the special causes.
At maturity level 5 you try to get a grip on the common causes by doing causal analysis using the measures/metrics/statistics, and doing continuous improvement and innovation.
Note that causal analysis is something that is often used, but at maturity level 5, the measures, metrics, and statistics play an important role.