Offering "Free for life" a good idea?

Is there anyone with experience in offering "Free for life" either from when they launched on ProductHunt or were just gaining early adopters? I want to hear your feedback/thoughts.

I know some popular newsletters took this route. After a certain amount of growth, the newsletter was no longer free. I am making Dewwy and I want to implement something similar where once I hit a certain amount of users, I begin offering a paid subscription.