During these school holidays, I enrolled my children on a swimming 'crash course'. Now, they could both already swim (my son about 10m and my daughter 50m), but I thought that a) it would help pass a week of the extraordinarily long school holidays, and b) improve their confidence and technique... and it did.
Both have improved, and I can only put it down to the fact that learning is focussed (one thing only is covered each lesson), applied repeatedly, reinforced and built upon. In their normal weekly lessons, the quality of the teaching is just as good and they put in just as much effort...but more things are covered and then for 6 days they don't swim - they don't apply and practice what they have been taught.
Now I'm a big fan of day long workshops, and still run them on a regular basis - there are a LOT of benefits in working with a group for a full day. BUT, the one drawback they have is that delegates often leave the workshop overwhelmed with new ideas and plans, they rarely experience proper follow up, and so they don't make as much progress back at work as they could and should. With a bite-size session, you focus on one thing, so that one thing is easy to apply, and it doesn't feel overwhelming.
If people attend one bite-size session a week for 8 weeks, they are far more likely to apply 8 learning points and action 8 things than if they attend one 8-hour workshop. It reminds me of the Sad Tale of Del the Delegate. So, if your measure of success for training is application to the job, I think that this is by far the best option.