They may even harm you if you take them when they are inappropriate. The whole community suffers when antibiotics are over-used, because germs become more resistant to treatment. Only Strep throat is treatable with an antibiotic. You must have a Strep test to determine If you have Strep throat. If you do have Strep, you must take an antibiotic to prevent Rheumatic Fever.
Many people stop taking their antibiotic when they start to feel better.
Not taking your antibiotic as directed or skipping doses may affect your ability to get better. It also encourages the germs to become more resistant to treatment. Many people don't finish their antibiotics, but save them for future use. This is a terrible practice for many reasons. For one, antibiotics lose their potency, often quickly.