Hi Friend, I'm planning to build a Quad using APM 2.8. I'm reading a lot on the board. But one confusion I can clear.  Its regarding powering APM.
There are 2 ways to do it. One is through Power Module (JP1 Open). Another one is through ESCs (JP1 Short). But I cant decide which one should I use. Why there are 2 different ways?     

if you use power module then you will get voltage data in APM (V and A) if via ESC then you will not get these data.

Power Module is better as it provides cleaner and more stable power.

Not necessarily. Most clone power modules have a lot of variance in the voltage output. For example, my logs show the voltage dropping to 4.3V sometimes and the average is only around 4.8V. I haven't noticed any issues in flight though.

As Satya sir said, using a power module gives current and voltage data to the flight controller, allowing you to keep track of it over telemetry and set actions for the APM to take when the battery is low.

There are a lot of complaints on the cheap APM power modules (PM) on the web, for the power supply. But it has a voltage and current monitor output you can send through your telemetry. Maybe you can disconnect the power line from the PM and power the APM using ESCs?

Yes you can
but using a saprate switching ubec  is better .