Yes -
1) You never know whether the crew may be under the aircraft checking something before releasing it. Leading edge devices can bite nastily.
2) There is push-back equipment that hugs a mainwheel to move the aircraft and it is best not to lower flap while it is attached.
3) If you do not get the 'ok' you are not going anywhere anyway
In any case, there is no panic to lower flap - why not wait?