With the current system of the 3 and 10 year bars, if you were an undocumented immigrant who left the United States to apply, legally, for documentation, you were denied due to inadmissibility. And even if you had US relatives the process was long to obtain a waiver. But, the I-601a made it that one could get a waiver prior to leaving and avoid the bar. However, this is not retroactive, and it only applies to those still in the US. The bar system needs to be reconsidered and/or updated, particularly when US citizen children are not allowed to request a waiver once the undocumented relative/s leave the US.
Presidential candidate Bernie Sanders has expressed his intention to do away with these bars.
So, let's get a head start now.