My horse has a sarcoid that, sadly, grew about 50%. It's on her joint, making it worse. However she's sound.
Look at the entire package. Don't fixate on the ugly unless it's definitely going to hold you back. If the horse has try and a good personality, blemishes or rehabbing is bearable.
Doesnt usually affect unless its in the tack area and then they can be rubbed by the tack whilst riding. Turmeric is great for sarcoids
I have never had issues with horses that have sarcoids unless they are in the way (usually girth area) otherwise I have never encountered a problem!
I bought my boy 7 years ago and he's only just passed away with something completely unrelated. He was 26 when he went - ripe old age :)
I work a horse with several sarcoids, it doesn't effect him at all, well except his appearance, they're huge, massive on on his neck and nose and the others around his chest. So if the horse is sound and happy, and you're not after a show horse, then I don't see why it would be a problem. I would buy a horse with one.