A bed frame's job is mostly invisible once the mattress and bedding are on — but the wrong support structure can shorten a mattress's life or void its warranty entirely.
Support type has to match the mattress
Mattresses are generally designed around an assumed support structure — a slatted base with a maximum gap between slats, a solid platform, or a box spring. Using a mattress on the wrong support type isn't just a comfort issue: many mattress warranties explicitly require a specific kind of support, and using an incompatible one (slats spaced too far apart for a foam mattress, for instance) can cause premature sagging and, in some cases, void the warranty entirely. Checking the mattress manufacturer's specific support requirements before choosing a frame is worth doing before assuming any frame works with any mattress.
Weight rating is about more than just lying still
A frame's weight capacity needs to account for more than a person's static body weight lying flat — sitting on the edge, getting in and out, and any dynamic movement all place more concentrated, momentary stress on specific points of the frame than an evenly distributed static load. A frame rated close to exactly a household's combined weight, with no real margin, is a less safe long-term choice than one with meaningful headroom above expected use.
Under-bed storage is a real space tradeoff, not free space
Storage bed frames add genuinely useful space in smaller rooms, but they typically sit higher off the ground and are heavier and bulkier to move than a simple frame — worth weighing against how much that storage will actually get used versus a simpler, lower-profile frame if storage isn't a real need.
The one thing people forget
Check the frame's actual assembled dimensions against the room and doorway paths before buying, especially for frames with a solid platform or footboard — some bed frames are surprisingly difficult to maneuver into a room or up a stairwell once assembled, and a frame that has to be built inside the bedroom itself is a real, sometimes frustrating, practical constraint worth planning for ahead of delivery.