First of all you have to be right candidate for tonsil surgery. Throat pain doesn't always mean tonsil problem. You must make sure while you have throat pain get your self checked by ENT surgeon and confirm that it is due to tonsil infection. If you have tonsil infection 3-4 times in a year for continuosly three years than you should undergo tonsil surgery. Or if your tonsils are so big that it causes problem in swallowing or breathing than you should undergo tonsil surgery. All surgeries are associated with complications but if you don't have any health issue and the surgeon and anaesthetist are competent than complications are rare. Tonsils are collection of lymphoid tissue responsible for throat immunity, but there are several other lymphoid tissue in throat so Tonsil surgery doesn't reduce immunity.
Tonsils have no immune function after the age of 3 years. Bleeding is the only complication of conventional Tonsillectomy. Please discuss new Hi-Tech options like LASERs or Coblation Wands to do the surgery. This is much safer and less painful as compared to conventional Surgical Dissection of tonsils.