The primary enemies of sealcoat are high volume traffic, forceful snow removal, heavy shade, and standing water/ice.
You will have some wear in the first winter. The amount of wear is largely dependent on the pre-existing condition, level of use of the asphalt, and surrounding conditions that might lead to early wear.
Some crackfiller will split in the first winter. How long the cracks stay sealed is largely dependent on the size of the crack and how much your ground shifts during freeze/thaw cycles. Because of this, there is no guarantee on how long the cracks will stay sealed. However, even after the crackfiller has split, it is still protecting the edges of the crack and resisting tangental cracking. Some cracks will split in Winter and re-seal in the Spring when temperatures rise.
Sealcoating is a maintenance act. While you may need to mow your lawn weekly, you only need to sealcoat every 2-4 years to effectively protect and beautify your driveway or parking lot. If you want that perfect look, it is OK to seal in back to back years, but this is not necessary for protection and preservation purposes. Avoid sealing in back to back years repeatedly.