During my group's recent run of White Plume Mountain in 3rd Edition, we encountered a scenario that brought into question the versatility of the Spider Climb spell effect. In the dungeon, one room involves a trap in which the floor is "magically frictionless", and the group is bound to slide around helplessly into traps. One player, however, tried to reason that he could use his Slippers of Spider Climb to help.
(There actually are Slippers of Spider Climb available to be found inside the dungeon as treasure, but by coincidence, the player already had their own pair. Nevertheless, the dungeon designers may have actually considered this.)
The reasoning is that a floor is not physically different than a wall, simply at a different angle. By crawling on all-fours, the adventurer should be able to activate the ability and stick to the floor just as they would a wall, moving at the typical 1/4th speed. As the DM, I allowed this clever use.
This got us thinking: What other uses does the Spider Climb spell have? How far does this ability to stick to things actually stretch? Using this logic, it would seem that it would grant a considerable benefit to balance checks in most situations where one might be thrown about. Granted, they would have to be prone for this to work, and most balance checks are done to avoid becoming prone, defeating the purpose in those cases. Still, scenarios where someone might need to keep their balance from being flung in a direction, such as staying on a boat in a storm, or holding on to a rampaging colossal creature, may apply.