In my view the potential benefits are:
1) Moving voting into the modern age, I think it is essential that ways of exercisig democracy keep up with techniology and the ways society operates in order to encourage people to participate.
2) Society has changed and the local community is less relevant to many people. Therefore they are not in the habit of using local facilities that might house a polling station. Online voting will engange these peopel and make them more likely to vote.
The main drawbacks of the process are:
1) Security concerns, one of the main ways in which electoral fraud is discouraged is that it would take a large scale operation that affects many polling stations or postal votes to affect the result of all but he most marginal Parliamentary Constituencies. Online voting would create the ptoential for hackers to commit electoral fraud in many constituencies at once and potentially affect the result of a national election.
2) The additional cost that would be incurred (see below)