When testimonials first started, footballers were only earning a few pounds per week, and so retirement meant unemployment and poverty for most of them. At that time, testimonials were a great idea to help them cope with difficult circumstances.
Nowadays, footballers in the top flight earn more in a week than most people earn in a year, so I think testimonials of that sort no longer have any justification.
However, I suppose that if the money raised goes to charity it would be a good way for the fans to express their thanks to Sami and vice versa.
Call me a miserable old bugger, but i find testimonials boring after the first few minutes and I haven't been to one for many years! 🙂