Understanding the removal of expired updates process

Can someone explain to me what occurs when I Edit the Membership of a software update and uncheck it from a Software Update Group? 

I thought unchecking it does what I need by deleting it from the SUG? 

I'm a tad confused about the need for a script if the Edit Membership process does what I need.

I read the following articles that state a built in SCCM task will run to remove the expired updates so I do not understand the need for a script:

• http://blog.coretech.dk/heh/sccm-2012-sp1-now-cleaning-up-update-packages-folders/
• http://www.mnscug.org/blogs/brian-mason/145-purging-expired-updates-in-cm12

I keep reading that other SCCM Admins are running scripts to remove expired and superseded updates, but I am having a hard time understanding the difference between the Edit Membership, Maintenance Task, and a script.

For instance, many SCCM Admins may be using a script such as this one to perform the expired update removal process:

http://www.scconfigmgr.com/2014/11/18/remove-expired-and-superseded-updates-from-a-software-update-group-with-powershell/

I just need someone to explain this to me, because I cannot find any info online. 

Thank you