Sync has positives and negatives.

Positive: You can basically party with anyone you want on any job, this would help me now with all my fighting classes 31+. Alot of new members in my shell I cannot even play with until they get to 25+ish.

Negative: As others said. You will stay at the best sp/hr spot basically the whole game no matter what peoples levels are. In FFXI once level sync came about the leveling camps where decreased by like 50% since everyone didn't want to go to X camp at X level because the leveling at the previous camp was on colbri and they are crazy squishy.

Over all I say it is a good system, but I wish SE would find a way to fix that negative if they implement it again.