It will certainly help to prevent the spread of new plants grown by seed....Just today, I pulled the flowers off some in the lane behind my driveway to prevent seed from forming and blowing around, thus dandelions becoming established in more areas.

But, these are perennial weeds that will remain and will come back each year if the weed itself isn't removed. So removing the flower is a means of control, but not complete elimation.

I gave up on pulling out dandelions. The tap is impossible to get out and they just come back regardless, so I'm happy instead to just pull the tops off and not break my back.

Pulling the flowers off dandelions will prevent the spread of the seeds from those plant but there are millions elsewhere that will still produce seeds that will fly in or be brought in by birds that eat those seeds.