Is it normally helpful if the doctor does a testis microdissection?

Not really: Unless indicated, this procedure is generally not helpful. It is a procedure for infertility that urologists or infertility specialists perform.

Micro-TESE: Microsurgical testicular extraction has a very special place in infertility. Men who have non-obstructive azoospermia (no sperm in ejaculate) may have sperm in the testes. The sperm are difficult to find and the micro-surgery allows the urologist to see the plump tubules that contain the sperm, otherwise the biopsy is "blind". Links to leading surgeons web: http://bitly.Com/zhfkp5.

Only for infertility: Only purpose is to obtain live healthy sperm for in vitro fertilization, usually by intra-cytoplasmic sperm injection directly into harvested eggs. Success rates vary. Only performed in the presence of non-obstructive azoospermia. More reliable & less destructive than obtaining sperm from a random testicular biopsy, where a piece of testicle is removed.

Depending...: Testicular microdissection is occasionally done to retrieve sperms for artificial insemination. And any surgery on any tissues or organs will result in permanent undesirable, yet expected, scar. So, surgery should not be done lightly but as the last resort for every illness after failing to respond to drugs, lifestyle, physical therapy, etc.