On one hand, when using RC patrol, it implies that autoreviewed users are autopatrolled on pages with pending changes, but not on others. This prevents regular patrol of those users (who often are merely autoconfirmed) on pending changes protected pages. On those wikis, the autopatrolled permission requires a much higher level of trust.
On the other hand, when not using RC patrol, but only NP patrol, it creates automatic log entries that appear weird to end users, since they're not for new pages. They're completely unnecessary.