Although we don't want to risk running out of data, most of us don't need much more than 5GB. You can get an idea of how much data you use by looking at your previous phone bills, or even by keeping track of the data usage section in your phone's network settings. Furthermore, you could also take steps to reduce your data usage, such as connecting to Wi-Fi when it's possible.
If you find yourself using more than 10GB, you might actually be able to save some money by getting an unlimited plan. Cheap unlimited plans are usually structured to deprioritize data usage when network congestion is high. This is due to a lack of premium data which aims to keep you connected at top speeds, as long as you haven't used too much data.
Deprioritization looks as if your network speeds get reduced for a short period of time before the network gets back to full power. This isn't ideal for someone who relies on their phone for on-demand high-speed data. However, if you just browse some social media or exchange messages with your friends and family, you may never even notice a change.