You get 70% of your salary paid like normal, once every two weeks.
You get paid 30% of your salary only IF the company meets its projections/goals every quarter.
That's crazy right? Would you take a job like that?
Bonuses often have 2 or 3 parts. Part 1 - has the company met its quarterly financial goals, Part 2 - has your department or business unit met its goals (financial or other relevant metric), Part 3 - have you met your personal goals for the quarter.
So it is not the concept but the wording that is odd. Your friend should make sure that he counts the 70% as the true base salary when deciding whether this job makes sense for him.
If I wanted to jeopardize 30% of my salary and take risks, I would start my own company.
Running a company involve taking risks that are generally only shared among the investors.
For this reason, I'm sure we're either missing details or the 70% is equal to around 90% of the industry salary which would be more acceptable, 10% off the base salary in exchange of 30% bonus, which would get you to 120%.