My LoR from my away was one of the most mentioned things on my app.
Whether or not doing aways for IM is worth it is up to a lot of factors. For me, my school was a low-ranked MD school with no home institution so I wanted to be able to have a LOR from a true academic institution to "validate" my clinical grades. I also felt confident in performing well on the eval given my performance during 3rd year. To top it all off, there was a big name (T5-T10) academic institution I could rotate at without having to move so it didn't add any expenses outside of the application fee.
So for me, 100% worth it but only because everything lined up well.