From chabad.org: Moshe is now commanded to separately count all Levite males from the age of one month and older. The three Levite families are counted, and a leader is appointed for each of the families. The total of all (non-firstborn) Levites eligible for this census: 22,000. The family of Gershon camped due west of the Tabernacle, and was put in charge of transporting the tapestries and curtains of the Tabernacle and their accessories. The Kehot family camped directly south of the Tabernacle, and was in charge of transporting all the holy vessels. The Merari family camped to the north of the Tabernacle, and they were in charge of carrying the Tabernacle beams, panels, and sockets. Moses, Aaron, and their immediate families camped to the east of the Tabernacle.

This sounds like a much tougher count, and one much less “useful”. while the first counted included all males between 20 and 60, this included all Levites, starting at one month old. While you could theoretically ask all males to stand in a line to be counted, you can’t do that with one month old babies and families. So Moshe had to walk by each tent, G-d told him how many people were inside each, and that’s how it was done. And all this had no useful purpose, other than to show the Jews how precious G-d thought they were.