True, but its nice to have a roomy bag for most of the trip. Agree about the space for souvenirs too.

Also, you may have a full bag and have to wear a jacket or fleece- but when the dirty stuff is compressed all of a sudden you can put it in the bag if you want.

Again, I term it a 'strategy'...gives you some options.

Finally, clothing is most efficiently packed when it is crisply folded. your dirty stuff will in fact balloon larger than when you left, unless you carefully fold/tuck/pack it...I dont like to deal with folding (and packing) dirty clothing. A compression sack will get it beyond ANYTHING you could do with normal packing. And obviously segregates it from the remaining clean stuff.