Officially, it's a tech demo to showcase what you can do with the data. Unofficially, crazies like me use it daily but need to fall back to other websites for various purposes:
- overpass-turbo.eu for data queries (showing all the tourism=viewpoint nodes in an area, or all the supermarkets, for example)
- OsmAnd for simpler queries like looking for a nearby bench while on the move (note that this also works fully offline, the only data it ever needs is for map file updates or if you want stuff like satellite imagery)
- OsmAnd for showing which of the fifteen bus stops across three areas my bus will actually be at. For example, this bus station has stop positions inside, outside, on the other side of the street with a traffic light to cross, around the corner... https://snipboard.io/DJUbVd.jpg It's madness, I walked up and down the whole area twice (took a while, missed my connection) before discovering the stop position around the corner, shown on the left on this screenshot. Had I just used OSM, it would have been clear where to go. Most transport apps don't show this, they just tell you to go and find H13 somewhere. Link to the bus line object shown in screenshot, btw: https://www.openstreetmap.org/relation/1514901
- map.meurisse.org for distance measurement
- maps.openrouteservice.org for more complex routing, e.g. with waypoints or time estimation with a specific maximum speed
- when driving somewhere unfamiliar or with a tight deadline, I'll fall back to google maps which is the only source of accurate traffic info that I know of (in NL there are loops in the road which are open data, but idk if anyone built a site around it, and with the public transport network I don't drive there often anyway)
To your specific question, OsmAnd can actually do public transport routing effectively in various countries using the data in OSM which is absolutely mind blowing impressive to me. But at the same time, I'm not sure why they bothered because without time table info it's pretty useless.