Edit: Completely misread things, I thought you had 192.168.10.0 and 192.168.20.0. Yes it would be the whole subnet for a /24, if you wanted less you’d go higher as mentioned.
192.168.0.0/29 would include 192.168.0.1-192.168.0.7.
/28 would get you up to 192.168.0.15.
No, /24 is just 256 IPs.
192.168.0.0/24 = 192.168.0.0 mask 255.255.255.0, or 192.168.0.1-192.168.0.254.
If you want 192.168.0.0 through, say, 192.168.7.254, you need to cover 2k ip’s, which is a /21. The mask would be 255.255.248.0.
A /24 would only be the last octet.



Telemetry is one reason.
Not having to worry about the service shutting down (Google Reader) is another.
Synced read status is a common one as well.
You may also use it in combination with another service to create RSS feeds for sites that dont have one.
Honestly having it not just get killed like Google Reader is a big chunk of the userbase.