The most obvious difference between Olympic weights and standard plates is hole size. Olympic plates have a 2 inch hole, while standard plates have a 1 inch hole for the barbell to pass through. Because of this displaced space, Olympic plates are slightly larger than standard plates of the same weight.
According to Addamantbarbell.com, standard bars will start to bend from a weight load of over 200 pounds, while Olympic bars, which are twice as thick, are safety rated between 1,000 and 1,500 pounds. A bending bar can create unwanted motion and make heavier lifts more difficult. If you plan to lift heavy over the long term, an Olympic bar and plates may be the ideal choice.
The ends of Olympic bars usually have revolving ends that roll independently of the bar. This is important in reducing torque during lifts such as the snatch or curl, when the weights are prone to spinning. Standard bars usually don't have this option and are susceptible to warping over time.
Olympic weights can often be purchased "grip" style with convenient handles built in to the weight. This not only makes the weights easier to move and store, but grip plates can be used for many dumbbell and kettlebell-style exercises. Most standard plates are not built with grips.
If you are planning to take weight lifting to the competition level, abandon standard plates as soon as possible. Olympic plates and bars are the only types used in competitions. To stay competitive, lifters in competitions almost always train with Olympic plates.
While standard plates can't be used on a Olympic bar, Olympic plates can be used on standard bars with inexpensive adapters, a financial consideration some may want to take when putting together their own home gyms.