If your garage door or your garage's walls currently have single-glazed windows, you should consider getting double-glazed windows for them. Here are two reasons why.
Any items you store in the garage will be safer
If you like to keep things like your out-of-season clothes and décor, as well as perhaps your paperwork and childhood mementos in your garage, then getting double-glazed panes for the garage's doors and any wall windows it has could be worthwhile, as this double-glazing could help to protect items that you leave in this area for long periods of time.
The reason for this is that double-glazed windows will, first and foremost, insulate the garage more effectively than the existing single-glazed panes. This means that you won't need to be as worried about the garage getting so cold and damp that mould starts to sprout on, for example, your winter clothes or your childhood drawings.
Additionally, double-glazed windows are tougher than windows with single glazing; this means that should anyone try to use a rock or a tool to shatter one of the garage door or wall's double-glazed windows, they'll be less likely to succeed and more likely to be noticed (due to how much force, noise and time it would take to break them). As such, provided the lock on your garage door is in good condition, adding double-glazed panes to your garage could reduce the chances of the things you keep in it being stolen.
You'll feel more comfortable in the garage when it's cold outside
As mentioned, adding double-glazed panes to the door of your garage, as well as to any windows it has will help to insulate the garage. This could make any long periods you spend in it in the cold weather far more tolerable and would mean that on any occasions where you use a portable heater in the garage, the heat from it won't seep through the windows.
This would mean that if, for example, you decide to spend a few hours reorganising the stored items in this space or using this area to work on a craft or DIY project, you'll be able to do so comfortably, without your hands going numb from the cold or without having to wear four or five layers of clothing just to cope with the low temperature. You may also find focusing on whatever tasks you do easier, due to not being distracted by the cold.