Astragalus is one of those herbs great for immunity. Everyone jumps up and down over Echinacea, but it isn't the only herb great for the immune system. I have been ill and has countless infections due to my health history with my stomach and my biggest pet peeve is getting sick. Since I believe in vitamins and herbs as well as various supplements, I rarely get sick and I really have to catch a bug to be down for the count. From what I have read about astragalus, this herb is great for a multitude of things and the benefits are great for those who have issues with:
Angina or Congestive Heart Failure
Colds and Flu (But don't use if infection is acute)
Weakened Immune System
Also, astragalus is great for liver health and adrenal health. If the liver is working, then everything else in body works better, because the liver is one of the most useful organs in the body. It's the body's filter to rid it of toxins and the storehouse to build healthy cells.
Of course this herb should be avoided when pregnant and I have heard that it is not safe to take with meds that have been prescribed after heart surgery or a heart attack. In fact this herb should be avoided if you take beta-blockers and if you had had any organ transplants. My experience with taking this herb has been positive. It isn't too harsh and doesn't have a weird odor :)