Whats the effect of irrelevant backlinks?

I realized that a lot here say that it wont hurt us or that there is no effect.
Why in hell are so many SEOs doing it then??? :|

 

I think there are several reasons why SEOs do irrelevant backlinks:

1. Some SEOs think any link has some value, so that 1,000 backlinks from general directories and such has more benefit that the effort it takes to get the links.

2. Some SEOs have clients who are looking closely at the number backlinks, and the SEO wants to placate his clients.

3. Some SEOs don't know the difference between a relevant link and an irrelevant one.

4. Some people have too much time on their hands or can't sleep at night, so they create irrelevant backlinks to fill the void.

 

Ouch. I think everyone has a different conception of "irrelevant." To some, it means 0 importance, to others, it means very small importance.