It depends. ERPNext is 100% Free and Open Source and depending on your scale and capability, self-hosting may be the right solution for you.
However, if you are a company, the cloud may make more sense for you. If you set up ERPNext on your own, you start with a base cost of around $40/month for a VPS, then you'll need to pay extra for email, security and backup services. After that, you'll spend a few hours installing and setting up everything, and also set aside a few hours of your time each month for maintenance + software updates, or maybe get someone to do that for you. Which gets expensive pretty quickly. Thankfully, our managed hosting service Frappe Cloud, takes away all of that so you can focus on what you do best.