Our office website has had 3 hosts already but the plan remains the same in terms of cost. Where before the bandwidth is a big concern, bandwidth is not an issue anymore because it has become cheaper. If our site would grow, I guess we have to upgrade our package. But it is somewhat stagnating at a plateau in terms of regular viewers although sometimes our site experiences a surge, maybe depending on the articles that are published on a weekly basis.
Hosting services should be upgraded on time ,You should upgrade your sites when you see such issues as:
Experience poor performance and site down time
When you want of Expand
You Start Getting Thousands of Visits Per Day
You are Facing Performance and Security Issues
I launched my website on shared hosting. Currently my website is receiving just about 500 visitors in a month. If I begin to receive more than 500 visitors in a day, I may upgrade my website, otherwise I am ok with the shared web hosting.
My website runs well with the plan which I subscribed into. But sometimes I am thinking about upgrading my plan so that I can use the bigger amount of space in terms of gigabytes so that I can upload a bigger file. But I also think that upgrading my plan is adding a cents into my bill. Upgrading your plan is good as long as you monetize your website, but if you do not monetize from it you better think twice before upgrading it.
I don't change my hosting plans to often because I know my site isn't going to cross the limits. I have an unlimited shared hosting plan from NameCheap. Only the bandwidth is unlimited the space and other stuff are limited. I have hosted two sites on same plan and both are working fine as they should do. Never faced any type of issues and the sites are always up and working fine.
It depends on the needs and earnings. If I need more storage/bandwith, I upgrade the plan. If I am earning a bunch of money from that website, I upgrade it to a dedicated server (or VPS) for more control and speed. One of my hosting plans is for idle sites with only 0-500visitors daily, it has 52domains in it and is still working fine with only 10GB of storage.
I upgrade my hosting plan when it is necessary to do so. This is why it is good to have a web host that you can communicate with as they will alert you to any problems or hiccups. I like to head off a problem before it happens if I can.