17jwblue17

In other words the seat chart shows me the minimum number of seats available. There might be more being held back for whatever reason.

Since I can reserve a seat, that means it is available.

It is statement like that which cause confusion. Unless he is messing with my mind. So essentially even if I reserve a particular seat, I might not be given it? Then what is the point of assigning seats?

That would be confusing. What if someone does not reserve a seat when they book? How would they account for that?

They would have to block a seat for every unassigned pax. That makes sense.

WineCountryUA

I think you are making this unnecessarily confusing.

If you can book a seat in a cabin and if a vacant seat is available on the seatmap, you can select that seat.

Does UA block seats for future assignment or other purposes, yes.

Do some people not select a seat at booking, yes. Note -- in the first line I stated it takes a willingness for UA to sell a seat (this is handled by Fare class buckets) and UA will limit the seats available for sale even if there are unassigned seats.

Do seat assignments get changed without notice -- yes, not usual but it does happen due to aircraft changes and other situations. This is a major nuisance but as all airlines will tell you a seat assignment is a request and not a specific guarantee.

Does UA sell a ticket and you might not be able to select a seat assignment, yes. This is typically a situation where E- is full and seats are available in E+, the passagner will end up in E- or E+ if necessary.

Does UA (and most other airlines) oversell / overbook and occasionally need volunteers to take another flight --- yes, Does UA very, very rarely involuntary denied boarding to someone -- yes, but very rare. (something like 1 in 10,000 -- pretty much the industry average).

You appear to have a fear of not getting a seat assignment, that is rare except for the above mentioned E- situation.
If you are concerned about a change in seat assignment, that can happen but is not common.
As for passagner loads, the seat-map is an unreliable metric for the reason mentioned in this thread.

blocking seat would prevent another passagner from selecting a desired seat -- Airlines handle this by reducing the fare class counter.

drewguy

+1. When you book the flight you select seats before paying. Any seat you are able to select is available at that time, and you can reserve it.

that doesn't mean you're guaranteed to get that seat at actual flight time, because equipment may change or other circumstances may lead to being switched.

But I have very rarely not sat in the seat I selected at booking, other than when upgraded or I chose another seat myself.