That is not a benefit. That is a description of what the software will do, but not why you would want it.

In case this seems like a pedantic point, consider the consequences of following a chain you aren't checking properly. You get SPV level security and might calculate a corrupted ledger. 

In the case of P2SH, I could make a transaction that spends someone elses money to myself. In the case of CLTV, I could ignore the locktime requirement.

Now yes, eventually, the miner majority will correct and uncorrupt your ledger for you. But by then it might be too late, you may have already acted upon the incorrect data by e.g. selling me lots of stuff that I paid for with somebody else's coins. If you don't care about that risk, hey, switch to an SPV wallet and save yourself a lot of disk space.

 

There isn't any difference in how long the divergent state exists for. That depends only on how fast people upgrade, which is unaffected by the rollout strategy used.