Windows 8 App Store App Install Path
When working on desktops or laptops most of us tend to create at least two partitions on the hard disk. Drive C, typically for OS and other software installation and drive D for our personal data. If drive C fills up or otherwise, we can usually selectively install applications on drive D as well. So in case of any issues with the setup, we can reformat just the drive C and not loose any personal data.
On our tablets and smart phones, we usually have options of using the Sim, the in built memory or the extended memory that we may install. This is typically a one time configuration and hence forth all market place installs happen on the selected memory device. The tendency here is typically to not use sim, but the memory device.
With Windows 8, since the focus has been to bring in tablets as well as a supported device, the App Store storyline has also gone the same way and there is currently no easy way to modify the path where the apps you download from the App Store are installed. By default they will land in drive C and all the app related data will also be in drive C only. So if you are upgrading your desktop or laptop, you would be no longer able to control the install path and end up taking up more and more space on drive C. While you can try to change the path, but it isn't officially supported as stated here.
Is it a big issue or not, is for you to decide. I, for one, will prefer more control on the install path at least when using Windows 8 on my desktop/laptop. On my tablet, I am fine with a memory device selection and let everything go there.