Bien sur touts les informations sont à disposition d'une maniéré ou une
autre pour les gps. Mais c'est pas le sujet.

Le sujet c'est *la communication entre des être humains*. Veut dire,
d'un seul coup d’œil tu as tous les information sur une borne et tu peut
les communiquer à quelqu’un d'autre, par ex. au téléphone.

That is IMHO not a sufficient reason to put such redundant information into the dataset. It is instead a reason to make an application (be it a program or a dedicated map rendering style or something yet else) that aggregates (or otherwise presents) that data in a way useful for human consumers. (Though, I dare say, when seeing the hydrant on a map, a human user can also easily see what streets are nearby. What they can't easily see on a map is whether the hydrant is directly adjacent to the street or nearby in the vegetation or in a tunnel under the street or in a building over the street and that's what the location tag is for, as Marc has pointed out.)

Some redundancy might be needed for practicability. (E.g. addr:street on buildings.) But in the case or nearby addresses of hydrants, it's just bound to produce data rot. Who's gonna update all hydrants when a street gets renamed?

Of course, if there's a little (foot)way connecting a hydrant to a street or building, however short that way may be, by all means feel free to map that way. (As an actual way though please, not as additional tags on the hydrant node.)

Regards,
Raphael