Tea bags are typically synonymous with lower quality tea. Much of the tea sold in grocery stores is sold in tea bags and is the very lowest grade of tea - tea dust. Although I suppose there are some health benefits to the tea dust found in tea bags, I doubt it is much. In my personal opinion, if you are drinking tea dust in tea bags from the grocery store, you are wasting your time if you are drinking it for the health benefits.
Because tea bags have such a negative connotation, the tea market has come up with another term to denote high quality, loose-leaf tea placed in a convenient single-serving size - tea sachet.
There is really little to no difference in the tea bag vs. a tea sachet other than the proposed quality of the tea, which is really the most important aspect. High quality online green tea stores often offer quality loose-leaf green tea in a tea sachet for those times when you are traveling or need the convenience of a single serving of tea. Since the tea is of high quality, typically loose-leaf as opposed to inferior tea dust, it is called a tea sachet to make a distinction of quality.
While traveling, I often take my favorite Japan Sencha Green Tea, Dragon Well Green Tea, or Jasmine Pearls Green Tea in a tea sachet. My wife and I take great care to make sure the tea sachets are of the right size to make sure the green tea has room to dance in the satchet, which is very important in display teas, like Jasmine Pearls Green Tea, which need adequate room to empart their flavor and antioxidants.
So, the next time you need high quality green tea while traveling, look to your favorite online green tea store to provide your quality loose-leaf green tea in tea sachets and try to stay away from the tea dust often purchased in tea bags at your local grocery store.