As with any test, statistical measure, or data point, the user has to be a cautious to understand its limitations. For example, the unemployment rate only measures folks who have looked for a job recently. It doesn't measure those who have lost hope and given up, or those who would like to work more hours and can't find them, or those who have taken a pay cut to stay employed. But those limitations don't make the unemployment rate a useless, dangerous statistic. The number helps tell a story (especially when used with other stats) about economic health.
The limitations of personality tests is that they are never a perfect match to an individual personality. We are all shades of grey with our preferences. These tests serve to categorize general preferences and provide some parameters. And we do change over a long period of time. Someone may naturally become more introverted or extroverted over decades due to their particular environment.
I have found personality tests useful for self-awareness. By taking a personality test and carefully reviewing the potential weaknesses, I am more aware of potential failings that may occur. For one example, I am able to make decisions quickly and lack patience for those who cannot. Awareness causes me to actively look for situations in which I may be acting impatiently. Another useful feature is that personality tests breed understanding between people with very different personalities. By understanding others better, I can thereby minimize my own largest weakness, the aforementioned impatience. And perhaps most importantly, for spouses, it provides a vocabulary and a paradigm to describe and solve potential differences.
My own wife laughed out loud when she read my personality type, nodding her head at some of the descriptions. And I smiled as I read her profile. Sure, these profiles might change over time as we mature, age, and experience new events. No, they are not perfect matches for us. However, for the time being, we both gain a little insight into what makes the other one tick. That is a good thing.