system
Given the following post, respond as if you're commenting on Reddit:
human
[General] Are there any logical reasons for ship boarding and land invasions to be a viable tactic in the age of sophisticated defense technology and orbital weaponry (other than entertainment purposes).

What I mean is how are 'tactics'  like space ships ramming each other (like in Star Trek Nemesis), and ship boarding (like in 40k) a viable tactic?

In naval warfare, ships should be around thousands of kilometers from each other at minimum. So to begin with no one is at a distance to be ramming each other and sending boarding crafts. Even if the boarding crafts do enter range it's hard to imagine them getting past a ship's CIWS or shields for that matter.

Of course there are exceptions like stealth boarding craft, or teleportation. But at the vast majority of times (like in 40k, and Star Wars), normal boarding crafts are the norm. 

Now for land invasions, other than to secure HVTs or minimize damage to infrastructure, how is orbital bombardment not the norm for planetary warfare? Let's take the Battle of Hoth for example. I think the decision to invade Hoth went like this: 

"Hey Empy P there are some rebies in some remote ice world called Hoth, how bout we blockade the planet and blast em with our cannons from orbit for a couple of days then send our AT-ATs to clean up" 

"NOOO you send AT-ATs NOW" 

.....

Or how the Imperium in 40k, whose ships carry virus bombs and other planet cracking weaponry, don't use said weaponry (or smaller scaled weaponry not necessarily exterminatus grade ones) more often. 

Orks in that ridge? Lets send SPESS MEHREENS! Great, now we've lost the Celestial Lions. Invading a Tau planet? We've 'exterminatid' planets for lesser reasons but how lets stage a land invasion anyway and hope 500 lasguns can diddly their way through Crisis Suits and Riptides. 

Of course I'm not diminishing the entertainment value of the aforementioned (and other similar) engagements. But I really just can't wrap my head around them without getting a headache.
gpt
I think that there are very simple explanations for both. 

Boarding: There are a few reasons for this, but here are a few of the more common ones. 

- There is something on the enemy vessel that our protagonists want/need and vica versa such as an artefact, a prisoner ect. Think the Star Trek movie, Star Wars episode 3 and 4. As such simply blowing the other ship out of the sky is not good enough. 

- Our protagonist's ship isn't as advanced as their opponents, but their daring crew members are better fighters. The Ultramarines novel is a great example of this, the Space Marine Thunderhawks can't keep up with the light Dark Eldar craft and so in a standard space battle they get crushed. But by boarding they have a much better chance since the Space Marines are superior to the Dark Eldar in the closed in corridors where the Dark Eldar can't maneuver. 

Orbital Bombardment: Again there are a few explanations for this. 

- The defending force may have the technology to prevent/survive such a bombardment. In SW episode IV they expressly state that they want to bombard Hoth but can't because the rebels have a shield generator. That was the whole point of them destroying the "shield generator" 

- Orbital bombardments aren't that effective. The antagonists can simply hide in bunkers and come out just fine. You will never 100% beat a prepared enemy with just bombardment. Just look at the Vietnam War or The London Blitz.