Servers are similar to your computer. And just like your machine, they have RAM (Random Access Memory) which is a resource responsible for processing user’s activities on your site. The more users you have and the more actions they take, the more RAM you’ll require.
And if your hosting plan can’t bring forward a sufficient amount of RAM to service those users, your site will slow down with pages downloading in a painful slow-mo. This will repel traffic, who’ll start leaving your site en masse.
Thus, it’s paramount to ensure your hosting plan matches your RAM needs.
How to assure you have sufficient RAM
First, if you are just starting up your site, you can just get a shared plan in place since we don’t expect that much of traffic to show up on your doorstep the next day.
Second, for an already running site, try measuring how much RAM you’re consuming today and might consume within 1 year. Transitioning to a VPS with an unlimited scalable RAM plan can be a good idea for making sure your site’s never slow in high-peak periods.