I can't say for other traditions or practices, but for mine certain workings require more time and more energy (compounding energy) for them to follow course properly. Those circumstances usually involve healing, major life changes, attitude shifting, raising awareness, removing personal blockages/obstacles, etc... Things that never happen overnight in any circumstances and require more time and effort than other things (like divination or offerings).
So healing from major traumas then might be an example of a working that got repeated? That is something that would take a lot of work and energy to completely process.
How often and when depends on what it is, when it arises (in the midst of other world and life circumstances), and the amount of energy needed. It can vary from one casting a night, for x number of nights in a row (or days); to once every full/new moon for x number of lunar cycles.
So each repeated spell or working is different based on the energetic needs of the spell and working?
I don't share the details of my practice because it's not my right to do so, but I hope the overview helped to answer a few questions.

I thank you for sharing what you have shared. I respect people who don't share a lot of details about their work. It is their choice and their right to make that choice. I personally share quite a bit of my practices and experiences, but that is also because talking about it on forums and on blogs helps me process it better. So its a learning tool for me.
Any way. The answer to your question is yes. It does answer why some one might use a repeated spell format for doing a working. I'm currently doing a repeated series of prayers over my ancestral altar to build up some power and energy there. I'm also trying to think of the best knife or tool to use to strip the bark off a staff I am going to transform into a specific tool. In the process of making that tool I am going to be doing repeated prayers and consecrations/anointing and blessings to build power in.