Would you consider genericized trademarks to be beneficial or harmful to companies?

For those that don’t know, genericized trademarks are company names which have become synonymous with the products they produce. For example, people refer to any brand of facial tissue as “Kleenex” regardless of if they are produced by Kleenex brand.

I can see both sides of the issue, as it is always good to get brand recognition in any way possible, but also, it might just cause people to use your brand name when referring to another product that is a cheaper alternative.