Sometimes the intelligence score indicates useful things about a monster, sometimes I'll ignore or change it. Ogres are like five int which is beyond stupid, and I just wouldn't permit a 1 int PC even if it comes out that way in the rules.
Other times it suggests tactics and capabilities. Goblins have 10 int and I think 12 wis, which makes them much more dangerous than they're usually written. They can come up with any tactics an average human might, set up ambushes and chokepoints, identify the most visibly dangerous enemies (probably can't identify the power level of a wizard, but can tell a guy in full plate with a greatsword is more dangerous than a guy in rags with a knife, which a 5 int ogre will not), pick their battles
Which is completely contrary to how they're usually written, which is why I mostly hate goblins and never use them as written. The first encounter many new D&D players have is the four goblins in lost mines of phandelver, who stand in the middle of the road and then rush into melee with a group of obviously well-equipped adventurers who possibly outnumber them. It's stupid and it's not playing to the goblins' strengths, which they're absolutely smart enough to understand and use. The correct way to play that encounter, if we assume they have to fight and can't get reinforcements, would be to have them hide in the bushes and fire arrows, stick and move, and go for the softest targets first. They can hide as a bonus action so in the undergrowth they'll be a huge bitch to flush out.
Of course, if you played them like that, there's a solid chance they'd TPK your party. Goblin slayer sucks, but goblins are certainly orders of magnitude more dangerous than most adventures treat them.
Also, note that thing about identifying targets. Would a gorilla know that a guy wearing metal armor is tougher than one who isn't? Probably not, and an ape is smarter than an ogre. So am I supposed to conclude that an ogre doesn't know what metal is?
5e has a big problem with mechanics that don't jive with the world they're intended to describe. It's not as bad as 4e for that (bloody path maybe the most egregious example) but there's a lot of shit like that where a rule is written for a game purpose and doesn't make sense when you try to translate it into the Actual Existing World the game's rules are meant to represent.