Is circularization necessary?

[Oddible]

Why circularize in a destination orbit? Aesthetics? Will an elliptical orbit eventually decay or decay faster than a circular orbit? Do orbits in KSP actually decay if they're above the atmosphere?

[SargeRho]

I think a circular orbit is easier to rendevzous in. Orbits don't decay.

[madbadger2742]

If you plan on rendezvousing with it, a circular orbit is easier. If you're mapping with ISA or Kethane, you need a circular orbit for even coverage. Otherwise, no, there's no gameplay reason to circularize.

[Dave Kerbin]

If you intend to land somewhere specific (or even general, like the day side of a planet), then a circular orbit makes that a lot easier.

[Warhorse]

Well, circular orbits are easier if you're trying to do a rendezvous, and an object in a circular orbit moves at a constant speed at a steady altitude, which can be important for certain applications. Still, there are also times when you don't actually care, and others where you actually want an elliptical orbit; see, for example, the Russian Molniya commsats.

[Kasuha]

No, it is not necessary to circularize. Sometimes it even eats your delta-v unnecessarily. Circularization is good in many cases, though. It gets you to defined state and you can burn any direction with the same effect, which cannot be said about elliptic orbits.

Circularizing is also good idea if you want to leave your main ship in orbit and only send down a lander.

If the body has atmosphere and you don't care where you land, you can just aerobrake to landing.

If it doesn't have atmosphere and you want to land, you need to burn retrograde and your orbit will go through circular anyway. So you can stop there and look for suitable place to land.

If you're visiting one of upper Jool's moons, it's better to not circularize and use that elliptic orbit you get after aerobrake to reach the moon with less delta-v. It may take longer time warp to get an intercept, but rarely it's more than two orbits.

[TheReaper]

if you need to perform an orbital docking at the target orbital body, it makes things easier, also approaching for landing from an actual orbit than a direct crash trajectory, is more efficent

[Nibb31]

It only makes things easier conceptually. It doesn't really make rendez-vous easier if you are doing it properly.

[UH60guy]

As long as the periapsis is not coincident with the terrain, circularization isn't really necessary. It's a tradeoff between ease of maneuvers (precision landing, rendezvous, Hohmann transfers, etc), fuel, and orbital period (time spent waiting for a burn).