The Swim/Run Brick

It can't hurt. After all, the more exercise you do, the faster the engine becomes (or so says popular wisdom).

However, it is probably more useful to train in race format; readying your muscles and mind for race day. It seems to me that if I were to train backwards (RBS) every day and then do an SBR race, my body would be in for a nasty surprise, although I have no experience or data to quantify such a claim.

You might try using the time after your swims for a short (1 mile or less) sprint, i.e. running as fast as you can, pretending you are racing to T1 out of the water. I've had more than a few races where the jog from the water to the bike area was longer than I'd like, and I think that the shock of running right out of the water slows me quite a bit. So, if you can train yourself to push through that as fast as you can, the faster your T1 will be, and the larger the head start you will have on the bike.

Of course, post swim is also an excellent opportunity to practice transitions if you have a safe place to stash your stuff and your bike. 

I do them for planning convenience (swim/run day 3x/wk) and pre-race T1 training.  Both of the local tri's here have pier to transition runs of ~220 yards and ~270 yards, I've found it beneficial to my T1 times to brick a swim/run as part of training.  It's also a great way to warm-up for a good tempo/interval run.  When I was HIM training a while back I would run to the Y, swim, then run back home once a week.

I don't do bike/run bricks until it about 2-3 weeks before race day, then I'll do a couple short race pace runs just to help get out of T2 better.

It's called an aquathon, and I've done 3. One more to go. And I'm finding I REALLY like this race format. Not that I don't like riding (I REALLY like it), it's just a whole lot easier to not have to tote the bike/gear to a race site.

But in training, yeah, I've done some. Like you said -- run to the pool, swim, run home. I find I'm MORE than tired/hungry after these workouts.

x2...only substitute "in the ocean"/"along the beach" for the "lake" references.

If the swim/run format helps you get in more training than you otherwise would, then, yeah, it's beneficial. If it's just transition experience you're looking for, you could probably get the same experience by parking your running shoes, etc. poolside, getting into them quickly, and just running a few minutes around the pool or building. It might help you get used to moving quickly out of the water, and dealing with vertigo if that affects you when you get upright. But it's not the same as the tri format, so I wouldn't make a special effort to do that kind of brick unless I was training for a swim/run race. Just finish swimming, get on your running stuff at a leisurely pace, and head out for a run if that's when it's convenient. Personally, I don't think all runs should be bricks unless they have to be. A run-only workout is probably best for speedwork or a long run, because you're not fatigued and will probably get in higher quality.

 However,  if you're training for swim/run races (my favorite--in my neck of the woods they're called biathlons), it helps to do some substantial swim/run bricks to get used to the feel of running after a hard swim. For me, the challege is vertigo and some leg muscle tightness due to the longer interval between the run warmup and starting the run.  There are things you can do (ear plugs, but I can't stand them; getting used to running when dizzy, kicking harder in the last part of the swim, dynamic stretches as you start running) that can help with these issues.