I don't think it's a silly question, but I'm not sure what you assume about the impression it will create is correct.
Any electricity-use, non-safety, issues aside...
A porch light on during daylight can look like someone is sleeping all day and didn't turn off the light in morning. It can look as if someone has simply gone to work and forgotten to turn off his life. It can look like a lot of things if you think about, it. Obviously, it can look as if some just leaves it on all the time, as you do.
Signs of activity in a home are what are said to help keep away intruders. A light that never goes out isn't a sign of activity. There's only so much anyone can successfully fend off anyway, but if you think of it even a time isn't the greatest; because if someone is really paying attention it doesn't take long before a timer can become pretty obvious.
Of course, in some neighborhoods and/or with some crimes; people aren't always zeroed in one house for a long period of time.