Syed Balkhi doesn't recommend you use a developer license for your clients' plugins. He says you'd be leaving money on the table.
First you’re responsible to provide support. Should they contact the original plugin developer, they’d most likely leave frustrated.
Second, if you forgot to renew your license, now all of your clients will see an expired license notification in their dashboards (varies on plugin).
Lastly, the biggest disservice you’re doing is to yourself. Because you’re leaving money on the table.
Most clients would not have any problems buying the license if you explain to them why they need it. You can also build the license cost in your original proposal and purchase the license on their behalf which you can transfer upon completion of the project.
Not only do you get affiliate commission from the vendor, but you freed yourself from support / updates responsibility.
His reasoning makes sense, and if you do decide to include client sites in your licenses, be sure to tell them the extra value they're getting, and be sure to have them on a monthly or some other kind of retainer.