I found an article on howtogeek - how to reduce boot time using e4rat. But seems that article is very old and made for Ubuntu 11.04
Since then lot of new Ubuntu versions came and now we have Ubuntu 14.04. Is safe to try that method on Ubuntu 14.04 without making boot more bad or even making system unstable ?
New versions of Ubuntu have ureadahead enabled by default, which improves boot speed using the same broad method, but is more adaptable: it works for both HDD and SSD rather than just HDD, and it pretty much just works without any manual intervention, detecting when you make a change to the boot process, re-monitoring the boot process and re-compiling its cache.
They won't work properly together (probably what would happen is that e4rat would be ineffective when using ureadahead) so I'd recommend sticking with ureadahead.
I waited for answer, but it seems no one has any view to share. So without any fear I tried that method (link is in the question). It did worked, I didn't face any error.
My boot time was reduced by 10 seconds.
I measured my boot time by installing bootchart ( available in software center) before and after trying out that method.