Use it.
Peace of mind for trades is best, sure it cost more than a stamp. Ensuring your $15-XX amount trade isn't lost or knowing someone has actually sent their end will ensure much smoother trades with new users.
I've had mail lost by USPS and have had it also delayed up to 3-4 weeks.
I now use tracking for anything of large value that I CANNOT AFFORD TO LOSE.
Remember the advice of the trade FAQ: DO NOT TRADE WHAT YOU CAN'T AFFORD TO LOSE
PSA by your local Mod
Note that you can add insurance to them as well for high value you. The insurance is based upon the value of the package. I did this just today and with tracking.
Actually tracking is also flawed people can still deliver it to the wrong address and it will still show delivered iv had this happen to me
Or they lose the package, which has happened to twice so far, even with tracking
Insurance automatically adds tracking
I use tracking with higher dollar stuff. Taysby and Silent each had $150+ trades, and both had tracking. Tracking is good!