There are a few reasons for using fire glass in your propane or natural gas fire table.  The first one would be adding style to your table.  With many colors to pick and choose from, you can match the outdoor decor of your patio to the color of your fire pit fire glass.  You may find the log set that comes with your fire table looking a bit too fake looking and this of course will cheapen the look of your table.  When using fire glass you will usually have a lower flame which will usually give off less heat.  When using the fire logs, you will get the flame to crawl up the height of the flame.  The appearance of flames coming out the file glass will give your table a magical look as flames mysteriously leap from underneath the glass.  

Usually the flame of a propane or natural gas unit will put out a more blueish flame as the height of the flame will be a

bit lower.  Depending on the color of the glass you will get more refection.  Some people like to use white fire glass because it doesn't give off much of a reflection, but it will fit within the decor with more existing patio furniture.  Black is a favorite for many people because it will usually match the table itself and give off a more colorful reflection off the glass with the blue flame.  These are the two most popular colors.  You can try experimenting on other colors like red, green, blue and other.  These colors can be used to spice up your table during the holidays.  Be sure to keep children away from any of the fire glass.  It isn't a threat to cut them with the pieces, but the colorful pieces may be mistaken for candy and will pose a choking hazard. The fire glass does take 15 to 20 minutes to totally cool off, so it can also be a burning hazard for small children that may pick up a piece off the table after the fire has been put out.  Enjoy your colorful fire table and spice it up with color.