Does climbing on roof cause damage/wear to roof?

I had my gutters professionally cleaned out, since I don't like climbing ladders. Their method was to climb on top of my roof (a regular slanted roof with standard 25-year shingles). I'm just wondering if this is harmful to the roof, or is that just a myth?
I can see why they do this, which is to save time. Is it standard practice for gutter cleaning services to climb on the roof to save time? Next time, should I find a service that does not climb on the roof?
Thanks.
Jeff
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On Thu, 24 Jul 2003 19:53:11 -0500, someone wrote:

That was no help at all to the guy's Q.
He didn't want to know how to clean his own gutters, he wanted to know if the method his contractor was using was harmful.
-v.
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