D&D 5E How often do you tell your PCs about other adventurers?

[payn]

If I am running a sandbox it comes up from time to time. Occasionally, if the PCs find something beneath them or not of their interest and pass, another party will take on the adventure. Sometimes that party fails and sometimes they are triumphant. Also, sometimes I'll have several parties competing for the same goal. In a more linear campaign, its unlikely to come up.