I went to add a symbol for a shelter along a trail. I had the latitude/longitude from my GPS, but couldn't find any way to enter the coordinates numerically. This meant that adding my symbol was this awkward dance of looking at two different maps in two different windows and trying to put the crosshairs in the right place. In fact, unless the thing you're adding a symbol for happens to already be captured by one of the available base map tiles, using a map & crosshairs interface seems like it's always going to be awkward for locating trail features.
It's also worth mentioning that users might want to upload a picture of the thing they're adding a symbol for and have the coordinates taken from the EXIF data. I know the site is already capable of this, as I've seen it in the photo upload feature, so hopefully it wouldn't be too hard to use this as a means to add symbols in a specific location.
Thank you so much for reaching out with some great feedback! I completely understand your frustrations, particularly when trying to use our base tiles in areas where the structure itself might not be easy to see. I think that having a variety of options for adding symbols would be best for everyone, and I will make sure that the information that you've laid out here is passed along to our development team. Let me know if there's anything else that I can do!