What the ?? Why are you guys fighting about whether trim should be used or not? The answer is - it's whatever the customer wants. Give your professional advice and let them choose:
- Metal trim does protect tile edges from casual damage, but frankly the trim can be damaged too. Metal not only scratches more easily, it can also be dented.
- Some purpose made treads (e.g. transition strips to tiled area from different surface, or stair trims) may be more hardwearing. But not undamageable.
- Any trim used against natural stone may not look right. The choice of natural stone as a tile is that it's natural beauty is inherent, and a well cut tile nearly always looks better.
- Some tiles (especially natural stone) may benefit from bevelling the edges - but most people simply want a perfectly flat floor.
- Trims used in modern tiled installations do look better in many cases. But not always. Beauty is in the eyes of the beholder.
- When you finish the work, you will probably never have to look at it again - but the customer will be looking at it every day.
I carry a Genesis set of sample trims when visiting clients for quotes. It gives customers the idea that pants plastic trim (pants looking and pants installed imho) is not the only option. But too much option often confuses people. I always make recommendations, and offer the good and bad points. But I always enourage them to make their choices. Some people will come to you with clear ideas, and specifications - that's great too, and sometimes it teaches me that another product may actually be better.
My point to all this rambling is that most of the posts I read here seem to say "its my way or nothing." You are all specialists and your opinions should be valued by the customer - but most (but not all - some cannot make a decision) customers will be far happier for making their own choices.