I have a site built in Drupal 6 that requires a number of blocks that are only visible to certain roles or on specific pages. Normally, I would use the block configuration settings to control page and role visibility. However I recently ran across the context module that effectively splits the site into "sections" or "groups" of related attributes.
My question is: When is it appropriate to control block visibility from context rather than the block configuration settings? Should I only use one or the other or a combination of both?
these are different approaches meant for different use cases, but they are not mutually exclusive.
context indeed splits the site into different contexts (and there is also the possibility of context types). and that is effectively its use case: context-based block showing/positioning.
however context won't check for user roles nor multilingual settings (i18n). block supports these cases (and you can combine both context and block to show something on a context depending on user role).
block also allows users to choose whether they want to see the box or not.
my final answer is: combine instead of choosing.