Meaningful interactions are good. Pointless ones are clutter. Having a special interaction for inserting a pen into a blender is just a waste of dev time and very few people are ever going to try it.
That's why it shouldn't be a
special interaction but a systemic one.
Object + blender = object turns into shredded material.
Pencil's material = wood.
Pencil + blender = wood chips.
Easy and systemic. You don't need to code a specific case here, the game will automatically give you the expected result by following its core physics rules.
Ideally, players will figure out some cool tricks the developers didn't even intend, just by trying out different things and seeing how systems interact with each other.
Thief's water arrows and torches are a great example.
Most RPG devs these days, and I wager Obsidian would be among them, would code something like this as a special case and make it very limited. They'd literally just script water arrow + torch = extinguished torch.
But in Thief, it's all systemic. Torches have a burning flame attached to them, which has the fire property. All fires have that same property. There's no systemic difference between a campfire, torch, or candle flame.
Water arrows produce a stim effect when hitting a surface: they create a water splash. Water splash extinguishes flame upon contact.
In some fan missions you can grab water buckets, throw them at a torch, and get the same effect (I don't remember if the original game had any water buckets, but the basic systems are all in place).
Instead of scripting something very specific, make a universal rule instead, and apply those rules to everything in the game.
Another example from Thief, every surface has a material property: wood, carpet, stone, marble, etc. It determines the noise produced when you walk over it or throw something at it, and determines whether arrows will stick in it or not. Every single texture in the game has a material, and level designers can just work with it intuitively. You made the windowframe wooden? Players can shoot rope arrows into it and climb up. Because rope arrows stick in every wooden surface. No need to script anything, just slap a wood texture on it and it behaves like wood.
The more complex these systemic interactions, the more interesting the gameplay, and the wider the possibilities for player experimentation.