Yeah, this is something you just make up to suit your needs.
Personally, I have mine grouped by type of device in ranges that would
allow for breaking them off into very fine-grained real subnets later
if I want to.  ie:
1-14
17-30
33-46
49-62
65-78
81-94
97-110
113-126
129-142
145-158
161-174
177-190
193-206
209-222
225-238
241-254

As you can see, I'm not using any of the numbers that would become the
network or broadcast address for any /28 network.

 - Tony Yarusso