In general, Trope Launch Pad items that are still getting regular attention from the person who initially proposed them ("original poster" or "OP") should not be significantly edited or launched by someone else without the OP's permission. This is because, while Trope Launch Pad items (like ordinary wiki articles) are technically free for any registered user to edit, they're also somewhat like a forum/discussion system, where you shouldn't edit someone else's comments at all.
The Up For Grabs tag indicates that OP doesn't care if someone else takes over with the writeup of their trope or sends it off to launch; it's in many ways the opposite of No Launching Please.
Do not add this tag to normal wiki articles (tropes or work pages), because we already assume everyone's free to edit (this is called Wiki Magic) — this tag should be used only in Trope Launch Pad discussions.
It is also a common faux-pas to start a new Trope Launch Pad entry with the Up for Grabs tag. If you're in a rush to get your new trope out to launch, chances are you're overlooking something important in the process (maybe it Needs a Better Name, or Yes We Do Have This One), which is an almost guaranteed way to get your trope pulled over in the Trope Repair Shop for reworking. You'll save the Repair Shop some trouble if you focus on writing a solid trope definition first; it's better to get a trope launched in good condition (no matter how long that takes) than it is to get it launched quickly.