This Behaviour helps to view time/date/timestamp/datetime from db to local Date / Time / Date Time format and in local Timezone. And save into db in with db timezone and db format. You only need to include this behaviour in models where need this facility.
With the adoption of PJax on Yii2 things have change quite a bit with GridView when it comes to work with them in AJAX mode. It will probably be confusing at the beginning, but then you will soon realize how powerful the new approach is.
With Bootstrap 3 and its inbuilt support in Yii Framework 2.0, you would see quite some new ways of creating HTML markup and styling your site. However, with version 3 of Bootstrap, tooltips and popover are not activated by default on your elements. Assuming you have activated the Bootstrap 3 tooltip plugin - how do you easily enable display of tooltips/popovers across your site?