[SalesForce] Infinite queueable chaining, what is the drawback

I've used this pattern in a number of projects to achieve this, by calling this from the finish method of the Batch Apex class:

private void reSubmitJob( )
{
        // try again in a minute
        Datetime sysTime = System.now().addSeconds( 60 );

        String chronExpression = '' + sysTime.second() + ' ' + sysTime.minute() + ' ' + sysTime.hour() + ' ' + sysTime.day() + ' ' + sysTime.month() + ' ? ' + sysTime.year();

        System.schedule( 'Scheduled Apex ' + sysTime, chronExpression, this );
}

Then, in your Schedule execute call Database.executeBatch() and abort the scheduled job System.abortJob(SC.getJobTriggerId()) to remove the 'used' job from the Scheduled Job list.

Note, Summer '13 gives you the System.scheduleBatch method which may also be useful for what you are trying to achieve. Though I have noticed some potential issues with that myself.

EDIT: one of the things to be wary of is the number of seconds you specify for your re-schedule. Sometimes, if this is too low (e.g. 30 seconds) the system takes longer than that to schedule it and the time passes and your job never runs. I've found 1 minute to be generally acceptable but have also been caught out with that on some occasions when I guess there is a lot of activity.

EDIT 2: this is not deemed best practice, see post Is there a simple way to serialize execution of Batchable class?. It's called 'suicidal apex' :D and should be used with caution.

First, the "backoff" feature apparently isn't implemented yet, at least last time I tried. See this question that I asked... no response from salesforce.com or anyone else, really. That aside, the answer to your specific is somewhere in the middle. It will not process queued items immediately as fast as possible, nor will it be once per minute.

Queuable items are placed into a queue to be processed at a specific time in the future, with a penalty applied for each call past the first in a transaction. The penalty is double the previous call's penalty, starting at 1 second, with some maximum cap. They'll be processed as soon as possible once the penalty expires. This means that you'll get better performance if you can process an entire trigger worth of records in a single queueable call.

Queueable jobs that "chain" are supposed to suffer additional back-off penalties, which doesn't seem enforced at the moment, but might change later. There's no real advantage to chaining instead of just spawning multiple jobs in a transaction, perhaps 4 to a batch (for example), if you need to. There are some limits to be concerned about, of course, outlined in the Governor Limits, particularly they share limits with future, batch, and scheduled calls, which are limited to 250,000 per rolling 24-hour window (or 200 times your license count if this would be higher).