Not caring about delay compensation, even if we're dealing about a few samples, can totally destroy your mix in one spot and can be ignored, sometimes up to a few hundred samples in another.
It's not just about timing issues that would only occur when you use plugins that induce a shitload of delay, but it's more about weird phasing that occurs due to delayed signal paths. Especially drums are prone to this, because you have a little of everything on every track. So make sure that those are sample-accurate aligned. To test the effect, simply duplicate a track and use the Time Adjuster plugin (or the Digirack Gate) to delay one of them by few samples. Activate/deactivate the delaying plugin to listen to the effect.
Without wanting to go into epic details about this complex issue, you can go the safe route and just follow some rules:
- Use the same amount of delay on every track (or at least on every group of tracks, like all drums, all guitars, etc.). The most simple way to do this is to put the same plugins on every track (or group of tracks), even if it is bypassed.
- In PTLE, deactivating kills the plugin delay, bypassing does not. This can be handy for manual delay compensation.
- Stay away from delay-inducing plugins on aux-tracks, especially those used for parallel processing (NY-style drum compression for example).
- Stay away from cascaded aux routing, like track-1 sends to aux-1, aux-1 sends to aux-2 etc. if you have delaying plugins on the aux-tracks.
- Using delaying reverbs can be OK on sends, if the wet signal is really 100%. Then a plugin-delay sounds like a reverb predelay.
- Delaying plugins on the master bus are always safe to use, because everything runs through them.
- If you're using a lot of delaying plugins (like UAD and other DSP-based fx) ATA will be your friend, but you still have to follow some rules, because ATA cannot heal what Digidesign omitted.
I hope that helps.