I am a generation player so aging on and letting go if my Sims is important. But as I am also a rotational player and as someone who HAS to have some control, I only have aging on in the household I am playing in at each time and have aging off for everything else.
I also play on longest lifespan (that the game allows without mods) and with 28 day seasons. I do plan on aging some Sims manually especially in households I don't play as much in and are mostly support Sims or secondary characters but I usually just let my Sims age up and yes, die when their time comes. I have even killed some intentionally.
Now, that being said, it doesn't mean that I won't feel anything when my favorite Sims die but it has to happen. It happened with both Sims 2 and 3. But I always reserve the right of keeping them on as ghosts and usually invite them into the household (usually via the cheats because I am way too impatient). Not all of them of course.