Wiping is only a security measure, once you clone or restore to another drive all data is either erased or written over, anything that was just marked as deleted will be taken care off by trim and garbage collection very soon after completing transfer. MR for instance will zero all used and unused cells. when clone or restore is started.
Wiping an SSD with a secure erase/sanitize/TRIM command is not
just a security measure. It allows the controller to proactively clear the NAND cells, returning them to optimal condition. If you were to simply overwrite a drive, without first performing one of these commands, the controller will be doing a ton of garbage collection (increasing write amplification), trying to preserve the not yet overwritten data. It won't know that the data it's working to preserve is mere moments away from being stale. Think of it like delivering a large shipment of furniture to a home and having to shuffle around existing furniture to make room, before being told that each old piece can be taken out to the dumpster. With secure erase/sanitize/TRIM you're told that all the old furniture can go, before you even start. In that case, you can either clear out all the old furniture and then bring in the new stuff or take out the old stuff as you need room for each new piece. Either way, you're not shuffling old furniture around inside the house. Does that make sense?
You're right that the old data will eventually be taken care of anyway but, by that point, it will have put a little bit of extra wear on the drive and possibly have slowed down the cloning process. I admit, it's not likely to make a meaningful difference in the life of the drive but why stress it unnecessarily. Since Macrium Reflect has the ability to TRIM the drive before cloning, all were talking about is making sure that box is checked.