What problem does this feature solve?

I can add markpoint based on max, min, avg points. But if I want to put value on top of each bar. If I am already using label in axisTick properties to show some values in the x-axis. So, I cannot use the label properties. In that case markpoint can be used for each bar value represent. It will be easy for use to understand the values on chart. As example attached mockup below.

What does the proposed API look like?

markPoint: {
data: [
{
value: 2,
label: "Jan"
},
{
value: 4.9,
label: "Feb"
},
{
value: 7,
label: "Mar"
},
...........
]
}