As others have said, no need to reinstall. However the downside of a rolling release distro is that you should really update all the time to avoid issues as no one is testing anything but updating the from the current to the most recent newer packages.

I have a PC with Manjaro that I am not using much and updating it after a few months of dis-use is always a bit of a risk.

Thus as a result you need a pretty good internet connection as weekly updates of around 1GB download are not uncommon with Manjaro.