Ditto to what Westwood has said.

While I HAVE actually witnessed fish taking the hook & being reeled in on a friend's larger, more powerful, higher resolution "fish" finder, my small unit packs more easily & answers my main need: to establish depth.  Am I in lake trout depth or walleye depth?  Tells me which lures to put on the end of the line or what water I need to move to depending on what I'd like shore lunch to  look like.

Having said that, in the interests of minimizing weight, I COULD be persuaded to leave my depth finder at home if I KNEW there were no lake trout present in the waters I would be fishing.  If there was a lot of portaging or bushwhacking involved, I might just leave it at home if no lakers were to be had [this remark comes from someone who has finally learned his lesson from chronic "overpacking" on bad-ass trips].

Jimbo   8-)