Lot has been discussed already, but a significant aspect to consider is the environment to which equipment is exposed. I'm recently out of over 40 years mostly associated with the US Navy industrial base (read: long term exposure to salt marine environments). Structural steel component rust, hydraulic cylinder piston surface corrosion, and long term water exposure are ongoing concerns, with the sun (UV rays) being somewhat less of a concern except in the desert areas (yes, the US Navy has those, too).
People have correctly pointed out that Deere dealers leave inventory outside (although most doesn't sit in a new tractor lot for long). Additionally, note that road grading equipment spends pretty much all of its like outdoors. Either way, there will be degradation over time. The question is, then, the costs of storage solutions vs impacts of those solutions.
Here's my short term take: For a couple of years in most environments, it's unlikely that exposure to the elements will degrade the operability of your equipment, although it may fade the paint, bleach the hoses, wires, and other plastics (only you can decide if that matters). Just don't leave it buried in dirt, or let it hold water. My primary concern would be hydraulic cylinders surface corrosion, as those are expensive to replace and once rust sets in there's no solution other than replacement. When not in use, keep them slathered with an element-resistant grease.
Sorry for being long-winded.