I don't understand the flow of sugar's targets/Contacts and campaigns.

Lets say I have 10 targets, in a target list and I send a campaign email. From the 10 two are invalid emails and two get converted into leads.

1. How do people handle the bad targets, ie. invalid emails? No point in always sending to an invalid email. What's the process to deal with them?

2. The 2 new leads are now duplicated. What do I do with the old targets? Manually delete them?

3. I want to keep sending my upgraded leads ongoing emails the same as the targets. So I have to manually add them again to a list?

This all seems cumbersome. How do other people use this? It almost seems like using targets is a bad idea.