What was the point of each verb/action in Monkey Island?

The short version: Back in the days not everyone had a two button mouse.

But besides that, there were clickables that offered more than just the default verb. The defaults are there for convenience.

For example, in most of those old point and click adventures, you had to specifically open or close a door. But you could as well look at it and you might even be able to just use it.

Surely you must have missed all the descriptions, which were often quite fun.

Apart from that, basically nothing, just look at how it has evolved in future versions.

BTW, are you sure you never used them? I find it quite hard to believe: could you use objects and combine them without using the actions?

If I recall clearly, you didn't miss much if at all. While there were many verbs, you didn't really need to use all of them. The times where you could have used a more specific verb (such as open/close) could also be done by the generic use verb now present in nearly all current adventure games.

There are only a few moments where you were required to use those "specialty" verbs in the monkey games as part of the puzzle (such as opening the safe by pushing/pulling on the handle). I believe there were also some comedic moments when you could pull on some things and you get a funny response or do something silly, but not absolutely required.

Nowadays, most of the verbs have been cleaned out. A lot of that due to the fact that it cluttered up the game and made it more difficult to grasp. All the more reason why many of those other verbs were useless and how the ubiquitous use verb remains.

The reason most of those verbs were there was due to the engine (SCUMM [Script Creation Utility for Maniac Mansion]) which was the base for most old Lucas arts adventure games. Since they were thought as necesary during the development of "Maniac Mansion" and removing them was more work than it was worth it, so for a lot of time those remained there as legacy code. Some of the verbs used in "Maniac Mansion" disappeared over time as they were redundant or confusing.

I think you had to use the flowers you picked in the forest (what kind of pirate picks flowers) use them on the meat from the kitchen then give that meat to the vicious guard poodles. Also there was the filling the grog from one mug to the other to melt the lock for the prisoner. I remember that one took my 12 year old brain a while to figure out.

Also picking up that stone idol under water, I'm almost certain you can't just right click that.

I can't remember any specific instances, but I do remember some of the absurd use of verbs gave some funny replies from Guybrush.