About a season after you run out of food the fortress dies. Everyone starves, goes crazy, and there's fun and games all over the place.
Having more food than you need is significantly less fun, saving your fortress' limited supply of it for spending on sunny days outside hugging goblins. With 100 dorfs, you should really have at least two years stock, or 2x4x100x2 = 1600 meals. No shame in holding 7 years supply like real medieval people did, at 5600 meals, in some 200 barrels and pots, feeding into smaller stockpiles near the dining areas for convenience.
Once you've got that though, stop gathering raw food. Turn off the food plots, disable the gathering zones, give Urists McFisherdorf and McRanger something better to do (like learning to use a spear and carry armour), and set about labouring on your latest project with all the new idlers. When food drops back under a couple thousand again (or whatever your two-year safety margin is), get back to producing it.
Food being hard means you can't ever ignore food. If I can't eventually ignore food (and clothes, furniture, and all the other basics one can rack up by the thousands), I can't get on with the more interesting stuff. Speaking of which, I need some bigger food stockpiles, and a lot more picks. Is everyone else buying the caravans with shellcrafts now the vermin-fish don't go extinct?