Are Multiple Channels 'Multiplicative'?

For the better part of a decade, marketers have been taught that it's a good thing to be multichannel.

In other words, it's a positive for catalog or e-commerce brands to branch out into new sales channels.

This may be true. It would've been foolish for a catalog brand not to start a website back in 1997. But would it have been smart or foolish for a catalog brand to open a chain of retail stores in 1997?