Would VS Would Have PP

It's a question of whether you're talking about something that happened in the past, or something that is happening presently.

There are fewer mosquitos than I would expect. (The expectation is happening right now.)

There are fewer mosquitos than I would have expected, but now I know it's because they just sprayed the area with mosquito repellent. (The expectation happened in the past.)

The would version is the more generic of the two, and can be used both for past and present pretty interchangeably. The would have version strongly implies the past.

When dealing with hypothetical situations, the wording affects whether you're talking about past or future.

My life would have been completely empty without you. (talking about a hypothetical past in which the person was never in your life)

My life would be completely empty without you. (talking about a hypothetical future in which the person is not in your life any longer)

Again, the would version can be used fairly interchangeably for both past or future, but the would have version strongly implies the past.