You know, when I was first thinking about getting an OL, I tried to make the decision with a calculator. I couldn't make sense of the math. Now that we have it, I'm really sold. I'm glad to have made the leap of faith. In fact, I've just ordered a second one.
It's all about the convenience of knowing that everything we need execpt clothes is there. And in some cases, clothing we only wear in the parks is there, too. No more forgotten items. No more doing without things because we don't have a rental car and don't want to spend Disney resort prices for them. No more throwing things away at the end of the trip, or not buying them to begin with because we knew we won't finish them by the end of the trip. (Perishibles excluded, of course.)
LOL, I'm going to get a real reputation as a drunkard, because I mention this in every OL thread. We also have several bottles of booze in our locker. It's nice to be able to enjoy a cocktail without paying $20 for it. (Not that we don't still enjoy a nice drink at the pool bar or with dinner every once in a while.) We'd have never had a bottle in the room before our locker because there's no way we'd go through even a small bottle during a trip. And there's no way I'd take an open bottle back home in luggage. With the locker, we can also have a little variety. I think I've got vodka, gin, and tequilla in there right now. (Proud member of the gurgling locker club.)
When we take a short trip with just the two of us, we never get a car and we always stay in a studio. For those trips, we don't do a grocery run. It's nice to have our stuff in the locker. There are some packs of oatmeal, some crystal lite, and a package of coffee in there.
When we're in a larger room with a kitchen, we'll either have a grocery delivery or make a trip to the Wal-Mart. That's our chance to re-stock. If I know we're running short on something, I might also pack it in our luggage.
There are also some nice-to-have things that I'd never pack in a suitcase, but I'm glad to have down there. A Brita pitcher, saran wrap, zip-loc bags, tupperware pitcher, kitchen knives, dishes, games, etc. I know I wouldn't carry them back and forth. I've also got an old laptop and router that stays down there so I don't even have to carry a computer case through the airport any more.