It seems that bikepacking bags are all the rage these days (frame bags, handlebar rolls, big saddle packs).
To me it seems that they are prone to moving around and getting in the way, and it also seems that they make the centre of gravity very high. I can understand it if using a bike without rack mounts, but otherwise - what is the advantage of using these things over a traditional rack and panniers?
They usually keep the bike narrow, suitable for trail riding where branches might snag panniers.
They use soft attachments (usually), so extreme vibration doesn't make undue noise or wear things out. There are people with damaged racks simply from plastic pannier clips bumping along on them for months on end.
Cheap "bikepacking" (with scare quotes) bags are cheaper than cheap panniers plus cheap racks.
Bikepacking bags also help packrats reduce their load, simply by being more constrained than large panniers.
They're also suitable for rental bikes, when you're away from home.
For road bikes, bikepacking bags are better for going fast since they are lighter and keep the bike narrow which helps with aerodynamics. This may make a significant difference going fast and far, as for example in Mark Beaumont's record-breaking speed run from Cairo to Cape Town in 41 days. Having toured on a road bike with both types of bags, I would add that the vibrations from a traditional handlebar bag can be quite annoying at high speeds, especially on rough pavement. By contrast, a bikepacking handlebar bag tends to be more snug against the bars.
While being faster, lighter, and more portable, I find bikepacking bags to be less straightforward to pack and access, and they typically don't fit as much kit as panniers.
I hang a tool belt over my handlebars because I can easily reach things in it, and because there is a definite advantage to having some weight on the front for steep climbs.
Another advantage is it's easy to take off whenever I stop so no one can take my expensive tools and I don't need an expensive lockable pannier.
Using a bikepacking bags is always depends on your choice. There is no rule that says you must or must not use a handlebar bag. But for those bikers who are planning to spend weeks, months, or years on the road, having a handlebar bag can really come in handy.
If you want to keep your essentials like camera, smartphone, your touring guidebook etc, a handlebar bag is the must for easy touring.
