What impact do PHP sessions have on Magento functionality?

My Magento store generates a whole lot of PHP sessions. I run a cron job to trim them back after they get to be a few days 开发者_JAVA技巧old.

Questions is this: What is the impact on user experience of having their PHP session deleted? Is there any? I haven't discovered it...

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Not really and as Jon Stirlng commented it will only terminate the session between the client and server. If user comes back new session is created. You can configure the session length from Magento admin