In the early days of mobile internet, data plans were relatively low. This is because our internet wasn’t quite as fast yet, and apps and media in general were still quite small. This meant that the need for a lot of data wasn’t there yet, and as such, companies such as Apple introduced limits where apps beyond a certain size could only be downloaded using WiFi.
Apple has increased the limits over the years, and they have recently done so again where they have bumped the previous limit of 150MB up to 200MB. Now, the difference of 50MB isn’t exactly very big, but it should open up the door to more apps that users will be able to download using their mobile data.
However, as 9to5Mac notes, some apps that are above 200MB can still be downloaded. For example, some games might be listed as having a file size of maybe 240MB, but because some apps are designed for multiple devices like the iPad, that’s how the file size can become inflated. This means that when downloading such an app on your iPhone, when it takes into account the files needed just for your iPhone, it might be below 200MB.
Your mileage may vary so it might not necessarily work with each and every app out there, but you can try your luck.