With Sale, Yarde is a (safe-ish) gamble on a quality young international winger who became available mid-season (rare). He wouldn't, for example, have been a panic/replacement buy because Charnley said he wanted out.
However, having signed him, this leaves Sale with these wingers vying for game time (listed in rough pecking order):
Solomona
Yarde
McGuigan
Charnley
Odogwu
Odogwu is a young lad, but a number of fans rate him more than Charnley based on his appearances last season.
The first 3 are all internationals, so Sale would need cover during the Autumn internationals (although Yarde has been left out of the England squad).
I would say (just opinion), that Sale don't "need" to offload Charnley, he's not surplus in any way. I think they're quite happy with their depth of wing options, and happy to keep Josh. I think any decision to leave would rest solely with the lad himself.