An even better reason to let your plant go to seed is to grow more cilantro. Cilantro is an annual with a very short life span. The best way to assure a steady supply of cilantro is to plant seeds every few weeks. You can harvest cilantro leaves about 40 days after seeding. A clump of cilantro will produce lots of seeds that mature in about 120 days after seeding. These seeds are easily harvested and also germinate easily.
You’ll collect a lot of seeds, so will need somewhere to store them. I store seeds in either Chinese envelopes I purchase at Asian markets or origami envelopes that I make myself. I actually make origami drinking cups instead of origami envelopes. I like the cups better than envelopes. After filling the cup with seeds, just take one of the flaps of the cups and fold it over the top to seal the seeds in. Tape to seal unless you want seeds spilled everywhere. The packets then go in the refrigerator. The cool environment preserves the viability of most seeds for up to five years.