When I started my first 3rd edition campaign all there was available was the PH, DMG, and MM. We played that quite happily for several years. Many of us were coming from decades of playing AD&D 1st Ed., and even if there were optional books available we would not have used them. We wanted to keep things simple.
When I started my second campaign, with a different group, they were converting from 2nd Edition with lots of modifications. So I decided to go primarily with the core three books, but with a supplement of races (mostly from Arcana Evolved), spells (from the WotC website and a book by Phil Reed), and Talents (a free extra 1st level feat from AE). I could have kept it at just the core books, but as the DM I wanted to add these things.
If I were to start a new campaign I think I would go with Arcana Evolved and use just the core books for that. I have never seen the need to add every single new book that is out there into the mix. It just makes things more complicated and dilutes the overall theme of a campaign.