When I was a kid, we had these big incandescent colored lightbulbs on the Christmas tree that always seemed a hairs-breadth away from turning it into a vertical yule log sans fireplace. If one burned out, you unscrewed it and then screwed in another. We even had fake candles that were bulbs hidden in the base with a liquid-filled glass "candle" above -- turn on the lights and watch the candle boil! Only one step beyond having actual lit candles on the tree, it's a wonder that whole neighborhoods didn't go up in smoke as the Christmas season rolled around.
Then we moved to the little bulbs -- safer, cheaper, and oh so much more frustrating. However, I figure if I can reuse them, then I minimize, at least by a little bit, how much goes into a landfill plus I save the $8-$10 that it will cost to buy a few hundred new lights. More importantly, I know that last year's string of lights works with the various ornaments we have that plug into the sockets and light up themselves. So I end up tempting fate twice...deliberately unplugging bulbs from the "never go out string" so I can plug in ornaments with flashing lights and, if I have to get new lights, never being 100% sure the bulb sockets on the new string will fit the ornaments I'm trying to plug into it in the first place. Such is the price one must pay if you're going to have a Christmas tree decorated by the U.S.S. Enterprise.
Additional compelling evidence that I'm a geek...it's the Enterprise-E hanging from last year's Christmas tree! When we get around to decorating the Christmas tree tomorrow, it will be joined by the Enterprise-D, a Borg cube, a Romulan Warbird, a Federation shuttlecraft (complete with Christmas greeting from Leonard Nimoy...yes, I know he's Jewish; you can discuss it with Hallmark), a Klingon bird-of-prey, Deep Space Nine, the U.S.S. Defiant, and, just for variety, an X-Wing and TIE Fighter from Star Wars.