I do log them to see what they are doing. IMO change or clean when they are not running right. But if it's not broke don't mess with it. Around 220k when I did my last TB Service. There was 5* difference between right & left intake cams at start up. The two cams even up when motor got up to opt. temp. So before starting TBS, I ran Gunk motor flush thru it for 10min. After TBS & other maintenance. Both cams was back in sync at start up.
Original Motor/VF-40 Turbo/15k OCI, Amsiol 0w-30 SSO & Ea. oil filters. Tuning Alliance Stage 2+, 18.5psi. Member; 200K + club. Currant mileage:244129