In the early days of Sitemorse a number of clients bought Page Credits rather than a Subscription and ran their tests on a ad-hoc basis around the time of any substantial changes to the site.  Not necessarily a bad approach but times have moved on.  Many organisations have greatly expanded the number of contributors to the site and decentralised control of the content.  So now there is often no detailed control of what content is added or when just an overarching policy or standard.

In this context taking just Page Credits isn't an effective way of keeping the quality of a website at an acceptable level.  Where as a weekly or monthly subscription runs regular reports that will maintain a consistent view of the key pages of the site identifying issues arising.  As part of a subscription clients get an allocation of Page Credits and a number of Full Tests to call off when appropriate (and the monitoring of a number of URLs) so that the combination gives a greater level of coverage and therefore a greater level of confidence in the quality of their web presence.

Several of our clients use some of their Page Credits on their test site which is also Internet facing.  In their cases all changes to the live site have to be made to the test site first, where they are tested and then made live.  So they run a lot of small or immediate tests as the changes are made to the test site.  Once they are happy with their testing and the changes pass the Sitemorse tests they are loaded onto the live site.  Their weekly reports test them again on the live site and they use Page Credits to do any additional testing on the live site where necessary.  In addition they have their key "landing" pages monitored.  Not surprisingly they are always at the top of their respective Sector Surveys each month.

I do accept that a subscription is not always economically viable.  A small number of our clients have sites under their control that are very small and have a very infrequent changes.  In these cases they use their allocation of Page Credits to run ad-hoc tests as and when necessary and this proves to be a very effective way of managing this type of site.

Oh and the other reason for choosing a Subscription over just buying Page Credits is that page for page a Subscription is the more cost effective.