Does subclinical hyperthyroid caused by graves always progress to hyperthyroid and is treatment necessary for subclinical hyperthyroid?

Watch carefully. Eventually, you will likely develop either overt hyperthyroidism, or you could possibly become hypothyroid. But not always, and this could take years. If you feel well, and your heart/bones/psyche/ etc are ok, you and your doctor (best: Endocrinologist) could elect to watch this and not treat now, but watch carefully.
Depends symptoms. Subclinical hyperthyroidism has low or undetectable concentration of serum thyrotropin (TSH) with free triiodothyronine (ft3) and free thyroxine (ft4) levels within normal laboratory ranges. Symptoms can include malaise, tachycardia, nervousness.Atrial fibrillation primary manifestation in elderly patients.Therapeutic trial of low-dose antithyroid agents for 6-12 mo. May help induce remission.