Fallout 4 is a game about choice. Whether you're a smooth talker or a trigger-happy psycho, a stab-happy serial killer or a 22nd-century cowboy, a ninja or a walking weapons platform and everything in between, you can do it all.
One of the more important choices you can make is whether you're really a Lone Survivor or whether you have another gun (or spiked bat, or chainsaw sword, or nuclear rocket launcher) watching your back.
Both have their advantages: having a buddy means double the firepower, having a pack mule and a friend with a particular set of skills that you may not, as well as full use of the Inspirational perk, which buffs companions. Also, a +5% Exp. gain isn't too shabby, either.
Being alone means that you don't have to worry about having an ally blow your cover while in Stealth (lookin' at you, Strong) or walking into your shot and getting hurt, as well as full use of the Lone Wanderer perk, which requires you to be alone.
A lot of the benefits come from the related perks, Inspirational (for companions) and Lone Wanderer (duh).
Roughly, the benefits are as follows:
(We'll assume you're at level 50)
Lone Wanderer:
- Take 45% less damage
- Carrying Capacity + 150
- Deal 25% more damage
Inspirational:
- Companions deal 20% more Dmg.
- Companions +25 Carrying Capacity
- Companions immune to friendly fire, +20 Resistance/+20 Energy Res.
On one hand, going it alone means a host of powerful buffs for you.
You take almost half damage and can carry a lot of stuff. The 25% damage boost is also nice, since it stacks with the boosts you gain from Sneak Attacks and perks like Mister Sandman, Cloak and Dagger, and Ninja.
However, if the buffs that Inspirational gives seems trivial in comparison, keep in mind that the impact of having a companion is not.
Having an ally deal 20% more damage might seem smaller than the 25% more damage you deal with Lone Wanderer, but keep in mind that arming your ally with a similar or better weapon than you have effectively doubles your damage output.
25 more carry capacity is certainly smaller than than 150, but keep in mind that 150 is the smallest carrying capacity that a companion can have. The range of carrying capacity among the companions is 175-275 (Paladin Danse is 210 unmodified), with all the relevant magazines and armor modifications.
So, do you tackle the wasteland alone or with a friend? I recommend a buddy, of course! Practical reasons aside, the Commonwealth is huge! While this means many things to see, fight, and discover, not every square inch of it is adventure. It helps to have a buddy along to break up the silence of travel or exploration when you've had enough of the same few tracks from Diamond City Radio. They can also open up new avenues of adventure, as some of them have personal quests that you can complete.
On the practical side of things, they also function wonderfully as pack-mules, with their huge carrying capacities to enable your hoarding and while they might occasionally blow your cover, they also work as meat shields or distractions. Not to mention that companions have a magazine almost dedicated to them, the Live & Love series, which buffs them even further.
However, if that's not the story you want to tell or just find their (sometimes repetitive) dialogue annoying, then you can have the best of both worlds.
Want to be a one-man army AND have a buddy watch your back? Then bring along your faithful canine companion, Dogmeat!
He doesn't count as a companion, so you get all the powerful buffs that Lone Wanderer gives you, but you still get someone to carry your stuff and attack your enemies. He also has a perk dedicated to him (Attack Dog) that allows him to grapple with enemies and make them easier to hit in VATS.
Sadly, other than the immunity to friendly fire that Inspiration (Rank 2) gives him, Inspiration has no effect on Dogmeat.
But hey, he wont judge you for murdering everyone in Diamond City in your underwear.