A search warrant is a just a finding of probably cause that the search will turn up evidence of the crimes listed on the warrant.
It's not that unusual to get raided without eventually being charged.
Getting raided is an extremely bad sign either way, especially when you're a worldwide celebrity. But I don't think a search warrant is necessarily an indication of already having enough to arrest someone. If there's enough credible people telling the feds that Diddy's electronic devices etc contained evidence of the alleged crimes, that'd be something they could use as probably cause to search his devices and properties. A premature arrest can only cause headaches further down the road when that person can afford the best lawyers.