• Skimming could improve the performance. 
• The advantage of major skim is that rules with Availability of 'Yes', 'Blocked', and 'Final' are carried forward. Rules with availability of 'No' (not available) or 'Withdrawn' are filtered out. 
• During a minor skim, rules with Availability of 'Yes', 'Blocked', 'Withdrawn' and 'Final' are carried forward. Rules with availability of 'No' (shown as 'Not Available' in the table below) are filtered out.
• Definitely, the rule maintenance would be easy esp. from not running into pre-requisite errors.
• After skimming, it is not a mandatory to delete the old rule set versions.
• Rather, we could point the application to skimmed versions.
• Again, having both skimmed & non-skimmed versions might take longer time during the packaging or deployment activities. (if we include)

Please also check below pdn link:

https://community.pega.com/sites/default/files/help_v83/procomhelpmain.htm#/express/tools/moverules/moverules5.htm