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 laptop overheating and shutting off components which also causes damage over time.
General performance of the PC will slow considerably after lengthy periods of time. As much as the Operating systems are better at running for long periods than they have been in the past certain processes will be started and never closed off correctly and will slowly eat into the resources of the computer. I would advise at the least doing a reboot 1 every day or so.