You must ensure you pull out the roots, or else the weed will probably re-grow. You must not allow weeds to go to seed, or else you are defeating your efforts. In the newsletter section of this website I share the weeding schedule I follow in my own garden. I break up my garden into sections, and weed just one section each week. It's simply too overwhelming for me to tackle the entire garden at once.
Grasses can be the most pervasive of all weeds.
Not only do they self-sow readily, many spread by underground runners or stolons, which are a modified kind of root. Most weedy grasses manage to find a way to break through any mulch or landscape fabric. Complete diligence is the only way to control them. If the roots remain in the soil, the weed will regrow. More information on the weapons you can wield to win the Battle of the Weeds.