I guess a disadvantage is the caffeine although the levels are low then coffee. Here are a couple of the advantages people believe mate holds :

• mate is a laxative
• helps digestion
• helps control your apittie
• helps imnunity
• fight aging and gray hair 

I personally think I not sure if it is all true though the mate affects people differently for instant the caffeine in it keeps me up unlike some of my other friends.

Here are some medical articles you can browse through.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11058886