[lkarsten]

Every site has something that can be cached. Images, js, headers, popular product lists, etc.

If a specific page item can be cached is really up to if the backend application takes cookie state into account when the page item is made.

The Varnish default of not caching anything when cookies are present is because we have no idea if the backend writes "Welcome back, krat0sprakhar!" when it sees the username in an incoming cookie. Sending that item to every user would be unfortunate.

Other than that, I'd recommend you evaluate your needs and not just pick a technology. If your page response times are low enough already, and your backends/appservers scale to as many concurrent buyers you think you need, you're good without Varnish/caching.

[jpp]

I'd add that edge side includes (https://www.varnish-cache.org/trac/wiki/ESIfeatures) can be amazingly useful. Even if you've offloaded all of your static content to a CDN, the ESI features of varnish alone can be a huge win.