Lets say I am invited to another company interview. As I see often the interviewers call you to come at normal working hours.
So then they assume that most companies can lets the worker go somewhere else during work time and worker might work those couple of hours at another not usual time.
But when you tell the boss you need to go, he usually ask why. So the question is how you should tell?
Or another situation - you got a phone call during work, you answer, and your boss asks - what did they offer or something like that. What do you have to tell?
I think lying is bad for your reputation and moral things.
Thinking logically - you have a right to check what you are worth. So there should be nothing bad to go to interview.
But I am thinking that it might be scary for the boss when you tell that some other company might be interested in you. On the other hand if the company is giving you value what you are worth then they should not be scary, if they are giving less than you are worth, then they need to fix the problem in themselves.