Should we write portable code?

Should we write portable code?

Should we write portable code?
Lots of software companies try to write portable code, apparently, this method could save a amount of time and energy to re-design code in different platforms.

However, with the development of mobile platform, mobile devices became more and more important, and the gap between these platforms is huge.  One portable code has to consider more and become larger to meet the different devices. What is more, comparing with the PC platform, the resources such as memory and storage in mobile device is very small. So porting the code from PC to mobile device is not a good idea.  What is more, the demand of customer of different platforms is different, it is not necessary to provide the same experience

Do you encounter such situations in your work? how do you deal with such issue?