In one relationship I didn't. I didn't really care if she saw her other boyfriend or not, but I did want her to make things well with her husband (it didn't happen). In another, I did. Her other boyfriend offered her things she wanted that I didn't give her (Grateful Dead, weed) and I was happy she saw him and felt like she was having her needs met, even though I didn't feel anything for the guy. She came back happy and relaxed and it made our relationship stronger.
So, yes and no. I don't think it's necessary, but it's better.