User blog comment:Alartan/Cooldown reduction is love, cooldown reduction is life!/@comment-25228021-20150301165652/@comment-24590723-20150301172221

In early stage of game cerntainly, mana is limit.

After Morellonomicon many casters keep spamming abilities like mad until someone kills them.

Some legitimate Riven's builds prioritize affordable cdr for her as a manaless champion.

It depends on game organization too - sometimes teamfight can happen around dragon in 10th minute, evolving into regular siege around 15th minute. But sometimes really, lane phase can last forever, changing into careful splitpush without any risky teamfights.