No, it will be 3 full sets. The SEPM then looks at what the client has, calculates the difference necessary to get that client from where it is to where it needs to be, and sends it that difference (or delta) file. That delta file is usually much, much smaller than the full package.
In looking in my own SEPM installation, in [SEPM install folder]\Inetpub\content\{C60D...} (32-bit definitions), I see the following:
full.zip: 115,403 KB (~115 MB)
xdelta....dax (the delta file created for my SEPM's client, which updates as soon as the SEPM does): 440 KB
I had my SEPM shut down for 10 days while I was out of office. My revisions went from the 21st to the 31st. The delta file built between those two for my SEPM's client was 2.6 MB.
The delta file can vary in size depending on the amount of difference, but as you can see, the delta is very much preferable to the full.zip in terms of size.
Since there are three certified definition releases per day, keeping three revisions essentially means a day's worth if the SEPM has the default LiveUpdate schedule of every 4 hours. People turn off their computers over the weekend, and suddenly Monday morning the WAN is flooded with full definition packages.
sandra