If you are unfortunate enough to only have access to mobile broadband or satellite broadband, then chances are you will need to keep a close watch on how much data you use over the month. These plans have a limited allocation (or quota) and you will either be charged excess usage fees, have your internet shaped (limited speed) or have no internet access at all, if you exceed your monthly quota. As a result it is important to manage your bandwidth usage, and there are a few ways to do this.
One of the most common causes of excess usage is system updates. In the case of Windows 10 PCs, these updates are mandatory and can be large, especially for feature updates. There is a way to prevent automatic downloads on Windows 10 by changing your network setting to a metered connection. Go to Start > Settings > Network & Internet > Wi-Fi > and then either Advanced or your Connection name. Set Metered Connection to On and you will now be prompted when updates are available. It is still advisable to apply updates regularly, especially security updates, but at least with this setting on you can choose when to download them.
iPhones and iPads are also bandwidth hogs when it comes to updates. These can be as large as a gigabyte for major updates. Apple does not make it easy to prevent these updates but if the pre-requisites aren't met then it will not download the updates. In particular, the device needs to be on charge and connected to a wifi network. Disabling wifi when you charge your phone is one work around. For other options take a look at this post (https://discussions.apple.com/docs/DOC-9741). It is possible to restrict automatic updates of Apps on iOS devices. This can be done by going to Settings > iTunes and App Store and disabling all the options under Automatic Downloads. This way you can choose to update Apps when you have the bandwidth available.
If your updates are not causing your bandwidth usage then it may be the content that you are downloading. Video streaming will quickly use up bandwidth, this includes the likes of Netflix, YouTube, Facebook and Instagram. Any site that shows videos has the potential to eat into your precious monthly quota so keep a watch on the sites you visit.
Unfortunately there is a big disparity between prices for data on mobile broadband and other forms of broadband. Until this improves, it pays to be careful about what is download over these expensive connections.