Wow! I never realize that it is a good idea using plastic in watering the roots of tomato and other plants.. I would love to try this out!

what are the advantages of using plastic bottle give me the brief idea about it

It's the slow "time-release" of the water, allowing it to seep in rather than run off, without spending the gardener spending the time over each plant.

Video:
http://www.todayshomeowner.com/video/diy-slow-drip-watering-system-for-your-garden/

There are Terra Cotta pots that do the same - Its an ancient practice.
We have become very wary of plastic since micro beads have been banned - very bad for us the little pieces of decomposing plastic. see here - http://tipnut.com/garden-irrigation/ and here http://irrigationpots.com/ Called Olla pots. - no affiliation.
I use the same technique to propagate cuttings,

a Small terra cotta pot with the hole sealed up inside another large pot filled with potting medium.
The small pot is filled with water that slowly releases to the potting medium keeping cuttings hydrated. something like this. http://www.leereich.com/2012/04/ten-weeks-ago-i-wrote-of-pot-in-pot.html

I believe it is called a "Forsythe Pot" https://www.agardenersforum.com/forum/ubbthreads.php/topics/120795.html