In general, the pooled approach makes sense when you have more than a half-dozen lines that appear on everyone's phone, particularly when you can group the lines into identical function. Does the user care which line they grab to place an outside call? Are inbound calls all of one kind? (Perhaps you need multiple pools if the answers are "no".)
The biggest problem we discuss around here is that the users have a hard time getting used to the idea. They will need education. With pooling, life is simpler for most call handling, but you can't "put line one on hold" and go pick it up at another phone. Users will have to learn to transfer or park a call. They won't (easily) have access to a specific line, but they shouldn't need it.. So, plan on spending some time with them, either using an Avaya education video, or a few PowerPoint slides, to explain the concept. And give some users some hands-on education in transferring and parking calls.