I'll echo what a lot of others have mentioned - Dynamos are great for commuter/camping bikes and the weight/drag is hardly noticeable especially on high-end hubs and lights. You
will notice the price though: $200+ for just the hub and $100+ for the lights (plus wheel build, soldering, etc.) and most bikes aren't designed/built with dynamo setups in mind, so it kinda detracts from the visuals if that's a concern of yours (lots of loose wires and such).
I do have a dynamo setup on 2/3 of my bikes. The third is a go-fast Ritchey road meant for sunny day rides and fair weather "go-fast" days. If its stormy, or I'm riding late/early I'll grab the disc rando bike with internal dynamo wiring and fenders. The light barely stays on when I'm going up some of the steep dirt pitches on my local weeknight rides here in the Berkeley/Oakland hills - on the road its fine though - anything about 5-ish mph and you'll be good with a son28 hub (or equivalent).
To actually give an example in response to your question, I did setup a bike with a dynamo and then eventually switched it out - that was driven primarily by wanting to have an unencumbered bike where it wasn't all utility focused. And the constant thought of saving about 400g
. I eventually went back to battery lights and was quite happy with it. I did have to bring a backup battery light on some longer evening winter rides though, but the extra hassle for 2-3 months out of the year was worth the lighter setup in the big summer riding days.