You will have some soreness and bruising for a couple of weeks after your operation. There are no lasting side effects after you have one testicle removed. Left untreated for even twelve hours, testicular torsion can cause permanent damage to the testicle, necessitating removal. Symptoms include swelling, pain, blood in the semen, frequent urination, and one testicle appearing higher than the other.
Having one testicle removed won’t affect your ability to get an erection. For most men it won’t affect their ability to have children. But for some men their remaining testicle might not work so well and this could reduce their fertility.
Talk to your doctor if having children is important. They might suggest sperm banking before having surgery.
You can also have a false testicle put in place so it looks the same afterwards.