I've gone from using regular lists almost exclusively to using tags and smart lists - they're so versatile. But I have a lots of tasks that aren't necessarily "real" tasks.
Things like grocery items, etc. These, I don't want to see on my main list.

For these tasks, I have multiple tags such as "+grocery", "+packing" and "+waiting". '

Notice that they all start with a plus sign? That's to make them easier to exclude from my main smart lists. So, instead of using this to exclude from the main smartlists:

not tag:someday and not tag:grocery and not tag:packing

I just use this:

not tagContains:+

This excludes all my items that aren't real "tasks", in one fell swoop.