And can u/what benefits if any to using diff definition files for same bin?
tunerpro doesn't know how your bin works at all. it's just a collection of numbers in certain places

so to modify your bin, tunerpro needs each table, constant, switch etc. to be defined so it knows where it's located in the bin, and also how to do some math so you're seeing something you can read '2000 RPM' instead of a raw value 0x1234 or whatever

a 'better' definition file might have more tables and variables defined, more accurate math, have them named better, have them in categories so they're easy to find, and might even have some notes built-in so you know how things work.

a definition can also have patches in it that change the actual programming in your bin, so a better definition might have more of those patches

usually there's a 'best' xdf definition out there to use for each bin mask since people work on them together, so it's more using the newest one rather than looking for the right one

this should be obvious but if you use a definition file not designed specifically for your bin mask it'll mostly be gibberish and you'll break stuff.