Question

Why do I see people implement properties like this?
What is the point of checking if the value is equal to the current value?

public double? Price
{
    get
    {
        return _price;
    }
    set
    {
        if (_price == value)
            return;
        _price = value;
    }
}

Answer 1

In this case it would be moot; however, in the case where there is an associated side-effect (typically an event), it avoids trivial events. For example:

set
{
    if (_price == value)
        return;
    _price = value;
    OnPriceChanged(); // invokes the Price event
}

Now, if we do:

foo.Price = 16;
foo.Price = 16;
foo.Price = 16;
foo.Price = 16;

we don’t get 4 events; we get at most 1 (maybe 0 if it is already 16).

In more complex examples there could be validation, pre-change actions and post-change actions. All of these can be avoided if you know that it isn’t actually a change.

set
{
    if (_price == value)
        return;
    if(value < 0 || value > MaxPrice) throw new ArgumentOutOfRangeException();
    OnPriceChanging();
    _price = value;
    OnPriceChanged();
}