Now we expect a desktop and a mobile app, also native and browser based. They all have different requirements. Even in the same category, such as iOS vs Android, some conventions are different. Having to write the app differently for each platform to make the best of it is not only expensive, but it may also be confusing to users who switch from one to another.

For example let's say you have a button on your desktop app that sees little use, but it is a nice feature for the few times it is needed. Because it is a desktop and you have lots of space and a precise pointing device, it stays. But for your mobile version, there is simply no room for it, so you remove it and tweak the workflow a bit so that it isn't needed anymore. Taken individually, they are both good decisions, but I can guarantee that the desktop user will complain that it is missing on the mobile app, and he would be right. It means you have to make a compromise you didn't have to make before.