When a severe thunderstorm warning is issued it means that severe damage from large size hail, very high wind etc is expected and can produce severe damage.
Sometimes the storm will go away without causing any damage or doing much so there's really no telling what damage may or may not occur when the severe thunderstorm warning is issued.
Sometimes severe damage may occur but other times just rain and some hail may come down.
We had a severe thunderstorm warning issued last night and was expecting large hail and high winds but we got the high winds and heavy rainfall but no hail came out of it or any damage.
Always be prepared to take shelter though in case the storm turns worse.