As long as they are secure, they can take a good bit of pressure. Personally, I use a smaller machine…only 2600 PSI. Using the pressure washer helps a ton with gutters, and yes, depending on the type of guards and the amount of debri, you can sometimes clean through the guards without removing them. This doesn’t work for every job but it can be great.
And I would really stress what @Luke just said about keeping off of the shingles. I’ve seen others completely pressure washing shingle roofing and it can look great, but BIG MISTAKE for them. Just keep it in the gutters and you’ll be good