I think it's better NOT to work ends in when donating to someone else for join. First, if the joiner work the yarn in when either edging or joining to another square; it's really not extra work. The only time I think it works best to work into the actual square before joining is if it's a lacy super open stitch. When you get squares with no tails you as the assembler really don't have a way of knowing how long the tail was, if it was cut.
There have been times when I received what appears to be a neat square/rectangle with ends tucked in to find as you're working with it, they've cut it