I’ve never personally liked playing a character that is lacking in the IQ department but then at the same time its probably quite fun to skillfully role play a character that has to have everything explained repeatedly by other party members, so your character can vaguely grasp the basics of life. For those though, that wish to play a character with a higher understanding of the world around them and to have the knowledge and lore of the ancients at their fingertips then it’s a safe bet that your going to want to invest in a high Intelligence score.
Intelligence is the attribute most used for people who wish to play a character who will be using magic in some form. The ability to recall information with an analytical mind and make quick mental assessments are the cornerstone of the Intelligence attribute. Imagine the scene. Your party is four levels down an old underground fortress abandoned years previously, yet the only way to go on is through a solid stone door weaved with runes of protection and just for good measure inscribed with an ancient long forgotten language nobody has heard of. Luckily for your party you happen to have the only scholar in that forgotten language in the world with you and thanks to their amazing mental aptitude they will easily be able to use their Intelligence attribute to decipher the language and dispel the runes of protection that quite possibly would have nuked the party on the spot if said wrong.
Did I mention spell-casting? In Middle Earth Role Playing the ability to cast spells is partly down to the spell lists learnt but also to the number of power points available to the caster. This number is got by using the intelligence attribute and multiplied by the level of the player character to get the final total, increasing as the character levels up (hopefully). Like most of the attributes mentioned so far, there are times when Intelligence is used in a saving throw, so if your mage happens to misquote the wording on fireball scroll a reasonable GM would allow you to make a saving throw based on intelligence (how badly did you misread it?) to see if it’s just your eyebrows you lose!