Unless your laptop is specifically designed to stay on for long periods of time then yes this will have an effect.
To start with components in your laptop that have moving parts will become over stressed (such as fans & HDDs) which will dramatically reduce their lifetime.
If you leave the laptop connected to the power the entire time it will begin to kill your battery life (leaving a laptop constantly plugged in often causes the battery to be unable to hold its charge hence why many people end up having to either replace the battery or leave it plugged in if they want it on)
Heat is always a consideration for laptops as well, if it doesn't have a decent amount of clearance around its vents the air will not circulate and lead the...