The concensus for KMC and Wipperman master links is that the link should last the life of the chain it's installed on but a new chain should have a new link. The "multiple-reuse" recommendation means it's OK to remove the link so the chain can be cleaned off the bike and the same link used to rejoin the chain after its clean.

SRAM does recommend not reusing their 10-speed master links even on the same chain once it's removed but there is no reason given. I've heard it's a patent issue, not a mechanical one. They make no such recommendation for their 8 and 9-speed links.