Two things: (1) it's hard to get a warrant. This is a search warrant for the President's personal lawyer's office and covers privileged communications (obviously under the crime-fraud exception). The federal judge that signed this must have been shown some very serious evidence of a crime.

(2) Since SDNY executed this warrant, it (a) had to be approved by the Assistant Attorney General of the criminal division (department policy for searching lawyers' offices), and indicates that a second criminal investigation of the Trump admin is active.

So, big big deal.