danoglide65 The microSD card contains a couple of partitions that include the base Raspbian OS, ZWO's extensions of the OS, device drivers, database of various forms, and two important files in the BOOT partition that is specific to a particular ASIAIR that is sold.
The BOOT partition can be read and written by mounting the microSD card on either MacOS or Windows. The other two partitions are in the Linux ext4 format and need Linux OS (or something like the extFS kernel extension for MacOS X which you can buy and add to MacOS X).
The BOOT partition includes two files: a file called zwoair_license and a ASIAIR_Config.txt. The ASIAIR_Config file is not strictly needed, but has your ASIAIR name, WiFI band, etc that is specific for you; but a default config file will work as long as your home network is not confused by the WiFi band the ASIAIR is using.
The zwoair_license file is absolutely needed to successfully boot the ASIAIR. It has an encrypted form of the processor ID that is unique to every ARM chip in a Raspberry Pi.
So, you can create a microSD card that has everything, copy the zwo_license file that is keyed to your ARM chip over and your firmware will boot up.
The microSD card is 32 GB in size. ZWO does not use the NOOBS like process to expand a smaller and compressed version of the card image on the fly. You need to copy the entire 32 GB image.
If your ISP is 1 Gigabit, it will take at least 32*8 seconds (4 minutes) to download the card image over the internet (longer if the server or your own router cannot handle the full gigabit speed). If your ISP only gives you 100 megabits per second, it would take at least 40 minutes to download. If you are running on a budget 25 Mbps from the ISP, it will take about 3 hours (in addition to eating into any monthly cap).
Additionally, you can obtain a license file from ZWO, so you don't strictly speaking need to save the license file. I don't know how long the automated process takes nowadays, but when it was manually operated, it took from two days to two weeks to get the license file back in the mail.
If you make a direct copy of the microSD card from an IMG file with ApplePi Baker, an inexpensive iMac computer takes about 3 minutes 20 seconds to finish the job, and you also do not need to copy the license file (unless you have only backed up one microSD card and you have two different ASIAIR devices).
So, the choice is yours. My recommendation is to make a copy locally (ApplePi Baker is a free program), just like you would save other important files locally.
Very likely, it is not whether you will need to create a fresh copy of the microSD card one day, but more like when you will need to do it, especially for people who do not use the ASIAIR soft shutdown process before powering off the device, or people who power the ASIAIR though a questionable 12V power source. Not to mention people who, even with the USB disk drive option today, are still using the microSD card to store their images and constantly plugging and unplugging the microSD card.
Chen