If you delete them all, and do nothing else, they will probably all come back.
But in the meantime, if you have shopped at a site, and go back, they probably won't recognize you. If you have Yahoo set up to automatically recognize you, it won't. Etc. You'll have to re-sign in to all those sites, and if you're forgotten your password, you may have to try to get it from them, or start fresh. So that may not be the best answer.
Your best bet, IMO, is to get a good cookie management program -- there are several, Cookie Pal from Kookaberra, it's shareware and costs about $20, is my favorite but there are other good ones -- and go through your cookies one by one. Delete all the junk ones, like Doubleclick, and all the other ad programs, leave only the ones from sites you recognize AND want to have recognize you. Then set up the filters. For each site, you can tell it whether to accept all cookies (your on-line bank or broker likely require this), reject all cookies (all the ad sites), or let you choose as they come up (the NYT, for example, has both required sign-up cookies and non-required email ad cookies. I accept the former and reject the latter.)
It takes a bit of time to get it all set up, but once you have it in place, it's pretty simple and non-intrusive.
And if I go to a site to buy something that I don't likely want to go back to, I let it set the cookies for the purchase, then when I'm done just go delete them -- CookePal tells you for each session what sites have set cookies and what sites you've rejected cookies from, so it's easy to manage. And i'ts fascinating to see how many cookies get rejected during a typical day!
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