That is a great question. Obviously the decision to upgrade or not is yours but here are some key benefits if you choose to upgrade.
You will always get the latest and greatest version of Office (through regular updates).
You will have access to a multitude of online version of your apps. (Excel, word, PowerPoint) meaning that from any computer with internet access, you can access these apps at Office.com using your credentials.
You will have 1 TB of storage on One Drive (this may be different from one country to another, I don't know enough). So all the work you save on OneDrive will be accessible from any computer with internet access. Even from your smartphone/tablet. You can sync your data from your desktop computer to OneDrive so you have access to the most up to date version of your work from anywhere. (I still suggest a good backup solution though as OneDrive may not be enough).
There are more benefits with o365, I suggest you go on office.com and do a comparison between 2019 and 365.
There is also downside to it. o365 is a service you need to renew every year or month meaning recurring cost as oppose to a 2019 license that you buy once and you're set. You may end up paying more in the long run for an o365 license rather than 2019.