When people look for names to buy and they mark the names they like, this creates a shortlist for them so they can review what they liked later. The more people that added your name to their shortlist the more it shows real buyers find your name interesting.
I heard some creatives also set names on their shortlist, so they can build lists of names to offer in contests from the SH inventory faster? Not sure why
But in the end, almost anyone can shortlist a name, if it's outside of a contest, usually it won't bring a sale
It's nothing. After holding a domain for 2 years on Squadhelp with hundreds of shortlists, it resulted in no sale and I have removed it from the platform.