Most likely won't boost earnings.

But remove units that make you negligible pennies in place of other networks or affiliates will probably be a better move.

Noone can tell you. Why don't you just try it?

It could for sure! See below for an explanation (hypothetical numbers)

Ad Unit 1 - averages $0.50
Ad Unit 2 - averages $0.40
Ad Unit 3 - averages $0.10

If a user is going to be clicking on an ad, you want him/her to click on Ad Unit 1 on the basis that it will pay the most. If by chance that user clicks Ad Unit 3, you get a click but it pays the least. Assuming you will get an average of 'x' clicks over a long period of time, you want them clicking 1 and then 2 in that order. So removing the third could possibly cause those same clicks now to divert to higher paying ones. There is a balance as you no doubt have noticed. There is also the possibility that the clicks that would have gone to #3 aren't going to go anywhere now, in which case you will come out on the losing end.

Run some experiments to figure it out.

^ Good point. But my units are all vertical so people clicking unit 3 all skipped the first 2 units... But then some people scroll back to the top of a page when they're about to exit which is where my main ad is... Hmm...

You need to test; nobody can tell you that. Too many variables.

Overall page weight is a factor. If you have script and graphic heavy pages, removing one ad will make everything load faster. The sooner the ads appear, the more likely they will get a click.