The segmentata, while offering superior protection, was very expensive. Often, you'd see veteran soldiers and officers wearing, since they could afford it. Also, the segmentata was a serious health concern. Due to the way the plates were made, certain movements can cause bodily injury(i.e. Lifting your arms above shoulder height). It could cause cuts, bruising, and could sometimes choke the user. The hamata was more common, although heavier, due to it allowing the wearer to be far more agile, and didn't pose the risk of self harm unlike the segmentata.
And, in regards to how long the segmentata was worn, I was reading in an old military history book from college days that there were soldiers wearing as early as 50bc to as late as 300ad. Whether that is true or not, I don't know. But, definitely it was worn by guardsmen and veteran officers and soldiers, for sure.