One third of Android users worldwide are still using Android 6.0, Marshmallow... followed by Android 5.1, Lollipop for a fifth and Android 4.4, KitKat for about 15%. So, good for as long as your hardware will support apps that are built and configured for later Android releases and increased RAM usage, as psionandy states. However, you will no longer receive Google Security updates which could leave you vulnerable to attack which is why a lot of users choose to install custom ROM's such as Lineage on Android 7.1.2, Nougat which are currently running Google Security patch for 05 JAN: 2018. My old Galaxy S2 and S5 have a new lease of life because of this.