Thanks for the reply Josh and it makes sense. This has only become a problem recently because each time someone converts to a trial subscriber coming from different channels at the same time or within a week, it's a problem for one of our marketing staff who has to add a start and end date for a trial and the campaign source and these are custom campaign objects in SFDC. So in our case, and for publication products only where trial subscriptions are concerned, only one channel should be given credit for converting and must be removed from the other channels once converted.
If it was a different product like sponsorship, advertising or database or events, it would not be a problem using multi-channels.
In our instance of SFDC, when you hover the leads or contacts campaigns, we see more than 4 campaigns that they are a member of, some from old campaigns. It gets verfy confusing for the person who does data entry.