The majority of web hosting companies (the old generation) are selling the belief that their customers are able to upgrade their plan at any moment. However if you think about it: it is not possible, because when a server is built or assembled, it has a certain capacity and limit. Usually the hosting companies just load up customers until the server reaches that capacity.
If you have a website that is running for the last 2 years, and you have now reached a point of popularity from which you need more resources, you will probably just overload your current server even more: the billing will certainly increase when you upgrade, but not the server resources.
There is only one solution to this: it is cloud hosting. This new generation of hosting is a revolution. It brings the ability to upgrade all resources of a server: memory, disk and CPU. With just a single reboot: you have just upgraded your server. No more overload. No more migration.
The market is catching up with this. Do not delay on making the switch: if you don’t, your competitors will it before you.