I'm new to FT as well, but I'm AA PLT Lifetime and use miles primarily for upgrades. If I'm on a short (3 or less hrs.) domestic flight I'll book Coach and use upgrade segments to move up to BC or FC (assuming I can get the upgrade), otherwise I'll tough it out in the back. For over Europe I'll purchase the lowest available coach and use miles to upgrade to BC. We're planning a China trip next year and will use miles for BC on CX to HK.

I used miles recently for a last minute LGA-ORD same day RT that would have cost $1,000+.

Oh yeah, my wife and I went to her kid's graduation on the West Coast last year; found out her ex-husband was on the same flight - immediately UG'd to FC. We both enjoyed waving to him as he went to the back!