The advantages of the gloabl level is that they are all in one place and easy to update. You never have to go searching through your marketing campaigns for a rogue lead score update. It's easy to use a token to make sure actions are counted equally.
I think the advantage of the local level is it's easier to manage conceptually, in that you say when this thing happens I want this to happen. For example, when a lead fills out a contact form, you send a response email, send an alert to the sales team, change the program success, edit the lead score, change the lead stage, etc. It can be easier to manage and keep on top of that way. It's also easier to assign different values to different programs, even if the activities are similar (for example one content download being more valuable than the other).
I personally do it at the global level because it's easier to see all of the lead scoring operations in the same place.
We did it at a local level because our regions were just so different we thought it would be difficult to find a scoring that worked for everybody. Plus we had a sense of each region owned their regional instances with us for assistance overseeing everything.
I executed this at the global level for common scoring items and have customized it per [local] subsidiary. This way, actions are consolidated where applicable, but when unique, it is tailored according to the subs needs. Also, when needs change for a subsidiary, we will collaborate and I can adjust the model accordingly.