Say you have 5 arrests warrants for members of a gang, you often can't arrest them all the once so here is where the "secret" comes into play when they are arrested and the arrest is maintained confidential for 24-48 hours depending on the jurisdiction.

This is done to prevent the rest from scattering into hiding as soon as the news of one or more of them getting arrested breaks, this also means they won't hold down somewhere and be ready for a fight, or even go and do something worse like take hostages in order to try to get out of dodge.

This also means that in some rights are withheld for the duration of the "gag order" like access to a phone or an attorney, however the police is not allowed to question or formally charge the subjects during that period either, so while there is some violation of rights it is not egregious.