(BRICK: Commonly, a combination workout that includes a bike and run back to back. Comedically, "Bike/Run It Can Kill" or "Bike/Run Ick". It can be any combination of triathlon sports with less than 10 minutes between sports. )
Saturday I did my first brick of the season with a couple others at the club. It reminded me how valuable bricks are, but that they should be used sparingly. What I mean is that there isn't much evidence that says you need to do bricks during the 'off-season' and then there isn't much reason to do them once racing starts either. During the active racing season on non-race weekends, you'll want to do some sort of brick workout depending on what period you are in (if periodizing your season). You can also do a mini-brick as a rehearsal a day or two before a race, but there isn't much value in doing bricks during the week if you just raced over the previous weekend, and plan to race the next weekend. They are fun and break things up, but once your body is used to the change, maintenance is all that's needed and if you are actively racing, you're maintaining your 'brickability'.
During the 'training' season, after the New Year when you official start training with purpose (January thru April ???), your workout time should be used wisely. Base training is the most important in the early stages, with gradual increases in duration (length of a session) and gradually increasing volume (amount of training time during a week) as well. Focus the time you have for a workout on one discipline--what I mean is, concentrate on quality, not quantity. If you have 1 hour to train, and you want to bike and run, pick one. Get in a good solid ride, or a good solid run followed by some quality stretching. No sense in cramming in a short ride and a short run. With that said, you do want to get in at least one brick per week starting about 3 to 5 weeks out from your first race of the season. If you adapt well, you can go with less (3?) and if it takes your body a while to get used to it, it may take more than just a few. I plan on racing in late April, so I may skip the bricks again till mid April and see how it goes.
With the above in mind, this can be tweeked by what you are training for: Sprint v. Ironman, for example.