You do not need to register for an account if you are only searching for and viewing planning applications. However, the new Planning Portal will offer a facility for customers to register to avail of enhanced online services such as commenting on live applications, tracking of applications, notifications about updates to planning applications you chose to follow, and submission of planning applications.
If you were registered as a user on the previous Public Access Portal, you will need to create a new account on the new site as previous user accounts are not being transferred across. The new portal will provide a guided registration process, along with helpful FAQ files.