Good UI design is all about effective communication. If you have a UI that is pretending to be something it isn’t (a person) then it is basically lying to you. That’s hardly good communication. It’s confusing and dishonest.
And believe it or not there are some users who won’t understand that it isn’t really a person. Some minds are very prone to anthropomorphizing especially when they are dealing with something they find hard to understand and unpredictable like a computer.
"Having a personality" is going to happen whatever you do.
Somewhat counterintuitively, this doesn't mean your interface pretends it's a person; but all copy is written by people -- words are used by people only (pretty much), directly or indirectly -- and the words chosen are projecting some personality onto the application whether you want to or not.
There are no words/phrases/instructions without baggage, connotations, etc..
I have no objection to that. I just don’t want those words written by people to make it sound like the application is a person. The app can talk about itself doing things (it does do things after all) but not as a human being with feelings and stuff.
And believe it or not there are some users who won’t understand that it isn’t really a person. Some minds are very prone to anthropomorphizing especially when they are dealing with something they find hard to understand and unpredictable like a computer.