In the race to the Patent Office, speed matters. You want to get the earliest possible filing date so that other patent applications will not be used against you as prior art.
If you’re contemplating international patent protection, you must secure a patent filing date prior to any public disclosures. So if you’re thinking of disclosing your concept at an upcoming trade show or product launch, promptly filing a provisional application gives you a filing date before your invention is disclosed to the public.