Any business person or someone travelling for a meeting or an event aka somewhere they have to be....wouldn't risk doing so as there is a good chance the earlier flight will sell out and they will miss it. Doubly so no FF status people as standby seats go in priority by FF status and they would frequently not get a seat. Not to mention the trade of for a standby seat on an earlier flight is usually a middle seat in back, one of the worst on the plane and separated seat for parties of two or more.
I know of people doing exactly this when travelling on airlines which allow gerring on earlier flights.
One of the benefits of having a flexible ticket is having the flexibility to just get on a flight when ready to go - where airlines allow standby type facilities / allow rebooking onto an earlier flight at check in , it removes a key reason to buy a flexiblie ticket and .... even worse... makes it harder for the passenger with the flezible ticket to be able to get on an earlier flight