Windows 10 Reset is a recovery option offered by Microsoft in Windows 10. For some reason, if your Windows 10 is not responsive you were suggested by some IT experts to reset your Windows 10 device. What Windows 10 reset does is, It will reset your PC to the beginning like a fresh new Windows 10 where you have to again install all of your software and application.
Reimage is the process to revise your Windows 10 device to a particular date or version. The image you use for imaging process will probably contain some files and software. So, when you reimage your device to using you will have to install the missing software.
There is a situation depend on the severity of your issue. Sometime reimaging your Windows 10 maybe solve your issue or not. When to use Windows 10 reset or reimage is solely depend on the issue on the choice you make.