Apple Business Manager is the underrated free service that makes everything else about running a Mac fleet easier. It's where you connect your Apple ID-based identities to your MDM, where Macs purchased from Apple or an authorized reseller automatically enroll, and where you handle volume app purchases without buying them on individual iTunes accounts. If you're running more than a handful of Macs without ABM, you're inventing problems Apple has already solved.
The setup, end-to-end, takes under 30 minutes the first time. You go to business.apple.com, sign up using a verifiable business domain (not gmail), confirm a few details about the company, designate an admin, and get an account. You then link your MDM (Jamf, Kandji, Mosyle, Addigy — any of them) by uploading a token from your MDM into ABM. Once linked, every Mac you buy through Apple or an Apple-authorized reseller, going forward, can be assigned to that MDM by serial number — so when the laptop boots up for the first time, it's already enrolled.
The second move is Volume Purchasing — buying app licenses in ABM, then distributing them to specific Macs via your MDM. This is how you get Slack, Microsoft Office, your password manager, etc., installed on every new machine without anybody typing in an App Store password. The licenses are owned by the business, not by individual users, which means they survive offboarding. Setting this up takes another 15 minutes once ABM is live.
If you bought Macs already, before ABM was set up, an authorized reseller can usually retroactively assign existing serial numbers to your ABM. It's a phone call, an email exchange, and a one-time inventory. After that, the entire Mac fleet — old and new — is enrollable, manageable, and operationally sane. Most companies we onboard don't believe ABM is this easy until they've done it. It is. Block out half an hour.