Before I moved to Keggles, I thought that I would stick with 5 gallon batches. Once I got my keggles, I figured that I have the capacity, I might as well use it. Yes, it is more expensive, but it does not take that much more time. If I am doing a beer that I have not made before, I will split the batch and expirement. Maybe a different yeast, maybe dry hop, maybe fruit or spice. If it is a house beer, I will just make 10 gallons and store the extra 5.
You are able to learn quicker what flavor profiles different things give to beer.