Traditionally I have run mostly homebrew adventures. I’ve used encounters taken from commercial adventures every once in a while. The Dragonlance campaign I’m running is the first I’ve really tried to run a module straight.
My players aren’t always going along with that idea but that’s ok. I’ve also added some content because I wanted a special event for the character with divine powers. I plan to do the same for the knight. Due to this I created Dulsi’s Dragonlance Addendum on DMs Guild.
For Spelljammer I found the process less satisfying. I had to tweak many individual encounters to match what I wanted. So running it requires looking at the adventure and looking my notes for things to override.
You pretty much have to, in my experience. The monsters are often optimized for min/max players, and if played intelligently will wipe a group focused on playing as characters with no knowledge of what they’re fighting. Also you always have that one player that reads the adventure (one offered to send me stats for a creature I had interacting with the party!)
I hate when people pre read the adventure, what’s the point of playing? I get it if it’s to guide someone new through to try to get them into the hobby, but that’s about the only example I can think of.