For me, I like to keep the herbs producing normally as long as possible, so I keep things from flowering as long as possible by cutting off anything starting to flower. Eventually, the plant will win and go to seed. Another method is to let just a few plants mature and seed - something I do with things I allow to reseed, like parsley, dill, and cilantro. Often, just one plant going to seed will provide all I could ever use in new plants. It's particularly beneficial for basil to be pinched back repeatedly, since it makes a more bushy plant with many more leaves for harvest. I never let my lovage or sorrel go to seed - the single plant is enough. I also refuse to let nettles go to seed (a disaster waiting to happen). Tarragon is hardly worth it - the plant grows by an expanding root that can be divided, but for me the one, continually growing plant is enough. Oregano grows profusely from root spreading, and seed is not necessarily the best way to get a good tasting plant - I could give away just about all the oregano anyone could want. Keeping it tamed is a problem, since it is related to mint. When oregano is in full flower, my wife cuts the flowers to dry for an outstanding wintertime tea, useful when dealing with colds and coughs - it also tastes nice.

Basil is an annual which means it dies after flowering and producing seed. Oregano's flowers can be used just like the leaves plus they are pretty. Let them flower away.

FataMorgana

If tarragon is flowering in zone 6 you should consider replacing it with true french tarragon which does not go to seed and has the superior tarragon taste. I let one large cilantro go to seed for coriander in kitchen and for seed bombing my beds... one cilantro plant can produce two cups of corander.. Also save basil seed because it's so easy, but bolting makes basil leaves tough and bitter, so better to leave only a few basil to seed. Some herb flower are fragrant and beautiful.... thyme, sage, lavender, coriander flowers fragrance is so so good after a hot day in the sun, and all attract pollinators to nearby summer veg.