Ok, image there is a situation like this:
Mary: Where is Bob?
Bod: I think he is at home.
According to this website, there are 4 present uses of present simple tense.
1: We use the present simple when something is generally or always true.
Ex: People need food.
2: Similarly, we need to use this tense for a situation that we think is more or less permanent. (See the present continuous for temporary situations.)
Ex: Where do you live?
3: The next use is for habits or things that we do regularly. We often use adverbs of frequency (such as 'often', 'always' and 'sometimes') in this case, as well as expressions like 'every Sunday' or 'twice a month'. (See the present continuous for new, temporary or annoying habits).
Ex: Do you smoke?
4: We can also use the present simple for short actions that are happening now. The actions are so short that they are finished almost as soon as you've said the sentence. This is often used with sports commentary, or in demonstrations.
Ex: He takes the ball, he runs down the wing, and he scores!
I would say the sentence "I think he is at home." falls to the Use #4 (an action is happening but stops immediately right at the time the speaker says it.
But see this sentence "I think chocolate is great", I would say this sentence falls to the use #2 (a situation that we think is more or less permanent.) or use # 3 (habits or things that we do regularly.)
But I am not sure I am right.