If you fail to do this, small problems will become very urgent and require a lot of sorting out. Whilst you are sorting out these small but urgent issues, loads of other small problems will be creeping up on you waiting to become urgent as well.
All this will leave you exhausted at the end of the working day and will do your reputation no good at all.
Those project managers that are really good at thinking ahead may seem relaxed and laid back. This will give the impression that the project was an easy one and this also will do your reputation no good.
So you have to spend time thinking ahead whilst making it clear that it is due to your expertese that things are going so well.
A big part of creating the right impression involves communicating with to your stakeholders and keeping them in the picture by whatever means they prefer.