Should Some Teeth Be Extracted Before Invisalign?

If a tooth needs to be removed in order to straighten teeth, it needs to be removed. If one uses wires or Invisalign, it won't matter.
The fact is, most cases don't need extractions. Years ago it was common to simply remove 4 premolars to make cases easier to complete. That practice is not as common, so odds are you would not need extractions for your case, whether with Invisalign or with brackets. That said, sometimes extractions are needed.
The only way to know for sure what is best for you is to see a dentist or orthodontist and ask.

If you already have spaces between your teeth then you have a spacing problem not a crowding problem so the chances of you needing any teeth removed is minimal. We don't like to pull teeth anymore and find that the patient is better off with a full set of teeth. Sometimes, wisdom teeth are pulled before, but its not necessary either.

Extractions were common with older methods of orthodontics. Most orthodontists today, due to new and advance technology, no longer need to remove teeth. Although, in some cases of extreme crowding, an orthodontist might recommend extractions. You should go for a couple of consultations and get several opinions. If your just looking to straighten the front teeth then Invisalign would be a great option. But if your back teeth do not align properly and your bite is off, then you might want to consider conventional braces or ceramic braces.

I will usually try other options (rather than extracting teeth) in order to achieve a great result with Invisalign. There are many ways to make space including expanding your arches, and creating small spaces between your teeth (IPRs). If you can keep your teeth, you should.
Exception: wisdom teeth -- If you still have your wisdom teeth (and all of your other teeth), the wisdom teeth should most likely be extracted -- ideally before you start Invisalign treatment.

Extractions for orthodontics is on a case by case basis. Only your dentist or orthodontist can answer this question. Please consult with your dentist to determine if this is necessary, it is not always required.