Another example: consider a company with two offices, each using about a dozen subnets, and an overall 192.177.32/19 address. A naive approach might be to assign even numbered subnets to the Washington office, and odd subnets to the Tampa office, so Washington would use 192.177.32/24, 192.177.34/24, 192.177.36/24, etc, while Tampa was numbered 192.177.33/24, 192.177.35/24, 192.177.37/24, etc. The most logical summarization scheme would be to have one summary for each office, but this addressing design precludes that! A better approach would assign 192.177.32/24, 192.177.33/24, 192.177.34/24 to Washington, and 192.177.48/24, 192.177.49/24, 192.177.50/24 to Tampa, so now we can summarize 192.177.32/20 for Washington and 192.177.48/20 for Tampa.
So, plan ahead for address summarization. Even if you're not presently summarizing, plan your IP addresses as if you were. Develop a likely summarization strategy, if only on paper, then assign subnets based on that design.