Well, in scrum specifically that's what all the rebalancing is about. You ask "does this amount of work make sense for the window we've got (2 weeks)" and if the answer is no, you add/subtract stuff as required.
I'm not saying it solves all the problems or has to be rigidly adopted to see any benefit, but I feel like it legitimately does address a lot of very common problems in software dev teams in a reasonably effective way.
Chunking stuff up into managable pieces has always been good practice for schedule management, all scrum does it provide a well thought out and consistent way of doing it. The caveat is you have to accept that not every task is going to fit into this model. Sometimes you need to just have a dev pound on something for a month until he figures it out, and breaking it up into "deliverables" just adds overhead, but I feel like if you can get _most_ of your stuff into a "small deliverable/demonstratable pieces" mindset, it's a good thing.