That's sharing their burden. Human beings need to share their joy. It's painful not to be able to share joy. At a wedding, you are there to share the bride and groom's joy. Not just to eat.
Shared joy is tremendous.
It makes it real, it makes it full. Ultimately, when we share even negative burdens of others, we share a sense of joy. Because helping people is indeed a pleasure. And when our friend overcomes his problem, the newfound joy is ours as much as it is his. Everybody wants to be a good person, to help humanity.