My view is that if it's not too much trouble to store, and if you know for sure that you'll use it it's probably worth getting on sale.
- Several years ago I purchased three pairs running shoes very cheaply at a going out of business sale. I'm down to one pair in the back of the closet upstairs now, but haven't regretted the purchase at all.
- I bought thirty sets of my favorite guitar strings when they went on sale at the music store about five years ago, and have been working my through them ever since.
- We've always got a pile of toilet paper, soap, toothbrushes, etc. kicking around in the basement storage area.
There's kinda a balance to be had though. We moved into our house five years ago and I nearly bought a water heater that went on sale (the water heater in our house is more than twenty years old), but decided it was going to be too much hassle to store (and what happens if I installed it after the warranty expired and there was a problem?). Five years later, that seems to have been a wise decision as the ancient water heater is still going strong. Same story with our refrigerator.
Don't buy a bike because it goes on sale. Besides being large and difficult to store, bike components change every few years (usually newer stuff ends up being better), and bikes go on sale pretty regularly. You might even find that the type of bike you're attracted to changes over time.