If you make a huge mistake and end up in jail as a result, you would hope that you might be able to pick up the pieces of your life after you get out of jail. Of course, in many cases it can be very difficult for past convicts to actually obtain jobs and even gain housing. This is part of why many people who have been in jail end up back there after release.
The only way to make it so that you will no longer be penalized for past mistakes, is to get them removed from your record. Expunging convictions can take these off of your criminal record so that employers and renters are unable to see them if they run a background check. This can give you a much better chance of being able to get jobs and housing.