What is the actual mean of Reconsideration in Google Webmaster Tool? Is Reconsideration compulsory after using Disavow ?
no, it is not compulsory. you submit a reconsideration request only if your site is banned, removed, or penalized by Google
As SultanofSEO pointed out, there is no need to use a reconsideration request if you haven't been penalised by Google, so if you are looking to disavow links that is fine, simply upload them through WMT and allow them to sit there for a while. There is a video of John Mueller that reveals that Google can take anywhere between an hour to a couple of days to realise that the list is present on the server but the actions (making the links act as no-follow) can not be sped up, instead you will have to allow time for the links to be crawled again by Google. Don't worry if you have already pushed the reconsideration into Google though, they have a system in place that auto responds to you if there is no manual action found on the site, so unless you don't hear back from them for a couple of weeks, you should be alright (the longer it takes to get a response the more likely it is that you have a penalty)
If you get penalized by Google or you got any bad links then you need to remove and apply for reconsideration.
Guys there is a clear misunderstanding when it comes to what the Disavow tool does... The tool is there for you to ask Google to consider the link within the list as being none equity passing (no follow) placements, it DOES NOT REMOVE the links from anywhere, you have to do that manually through contacting the website owners.