What is new in Proxmox VE (virtual environment) 5.2 - Should I upgrade?

Cloud-Init - automatic virtual machine provisioning

Cloud-Init will help you do initial setups on your virtual machines after its first boot. Cloud-Init is a multi-distribution automation software. It is similar to Puppet, Ansible, Chef, etc...

SMB/CIFS Storage Plug-in

SMB/CIFS (aka Samba) is a network shared storage usually used by Windows platform. SMB/CIFS is typically faster than NFS. It is also simpler / easier to learn due to its simpler username / password.
This is a huge feature and one that I have been waiting to arrive. As of currently I only use NFS for sharing network shared mounted storage inside LXC containers.

Let’s Encrypt Certificate Management via GUI

Let's encrypt has changed the SSL industry. Let's encrypt basically offers 100% free perpetual SSL. I am using Let's Encrypt for almost all my websites. Having Let's encrypt integration in Proxmox will be useful in cases where I can not install certbot or acme due to age of server issue, etc...

Proxmox VE 5.2 also adds many new improvement features for better usability, scalability, and security

+ Creation of clusters via the web gui. Now you can create and join nodes to a Proxmox cluster extremely simple and effective.
+ LXC management improvement: Creating templates or moving disks from one storage to another now also work for LXC.
+ If the QEMU guest agent is installed, the IP address of a virtual machine is displayed on the GUI
+ Administrators can create and edit new roles via the GUI.
+ Setting I/O limits for restore operations is now possible (globally or more fine-grained per storage) to avoid I/O load getting too high while restoring a backup.