Its done to keep the line from spinning on the spool during initial installation. But if it makes him happy, i'll say its for corrosion proofing, drag increasing or a secret fish catching method trick of the Mayan Elders
"Learn from the experts, you won't live long enough to figure it all out on your own..."
We use a non-absorbant hospital grade wraping tape on the spool prior to filling the reel (when we load spectra). This gives the line something more to grip on, less prone to move on the spool itself under load. While the tape does not absorb water, water still can penetrate to a spool. We're also doing some experimenting with parafin used as a base prior to putting on the tape. If someone is highly concerned about spool corrosion, Swifty's line removal and wash system provides a great means of insurance when used with regularity.
I use waxed rigging floss 2-3 passes when I start a spool then tie the rigging floss to the spectra. I have also been waxing the spools prior to adding the line, I haven't had any corrosion on the spools yet.
Could be a light weight, drilled spool and he's wrapping it to keep water out. I know Shimano says you don't have to do that even with the DC models. I put flextape (non-absorbant hospital grade wraping tape) on the spool prior to the spectra to help the spectra grip the spool.