system
Given the following post, respond as if you're commenting on Reddit:
human
[General] How effective are planetary blockades really?

I mean you would need to have ships positioned in orbit around the ENTIRE planet. If there are only ships around the equator for example, people can still theoretically take off and land from the poles or high latitudes. If you do completely surround the planet that is a lot of ships that aren't on the front lines or doing much else.
gpt
You can just sit in high orbit, someone taking off is going to do so in a predictable path to reach orbit. With lasers or solid munitions/rockets you can just shoot them down before they break out of the gravity well. 

One ship can cover a massive area. The ISS is in fairly low orbit and it has a pretty wide view. On the subject of orbits, ships won't be stationary in orbit. They will be orbiting, so 2 or 3 ships, with sufficient sensors and weapons range can keep a lock-down on a whole planet as each ships completes an orbit in a few minutes. Some could be over the polls and some over the equator or anywhere in between. You could also have faster response ships that can be deployed from larger ships to engage enemies picked up by orbiting vessels who can't engage them immediately if they have a blind spot.

TL;DR Orbits mean that a few ships can cover a large area in a very small amount of time. Taking off is also not a rapid or particularly stealthy process that gives blockaders plenty of time to detect engage them.