When I was very young I learned to fly fish from Richard Ricko, a well-known rod builder, fly tier and fly fishing ledged from western Pennsylvania. One thing he taught me was to dry and clean my fly line after each fishing trip. To this day I follow his rules: Don't put your reel underwater unless you have no other choice. Upon getting home, strip off the line you used that day and let it dry. Clean your line before you put back on the reel.
Taking care of your equipment is essential for maximum performance. I want my line to glide through the guides like it were brand new. It needs to float high in the water and allow me to pick it up and lay it down where I want it. I want to have as little disturbance as possible when laying it out on the water. Line that is left wet on the reel will soon develop cracks and have dirt build up that will shorten its life. Wet backing will soon dry rot and become weak. Cracked fly line will get waterlogged and sink. Dirt causes friction, which will make it harder to cast. Dirt also absorbs water and will cause the line to sink. This makes it harder to pick the line up off the water and it will land hard, spooking weary fish. Dirt on your line will cause the guides on your rod to wear thin and the edges will get sharp. Your next new line will become damaged from the sharp guides if undetected.
So many times I've seen people set their rod and reel down in muddy water or on the wet sand. Fishing from a drift boat, their line is often being stepped on or laying in muddy water at the bottom of the boat. But the very next day they are back with that same equipment, having trouble casting or complaining their line is sinking and their expensive reel is making a funny noise.
Start with a container of mild dish detergent and clean water. Coil the line from the tip into the soapy water. Let the coiled line soak for a short time. In a separate container with clean water, coil the line from the reel end into the rinse water container. Run the line from the tip end through a clean cloth. Let it dry for a bit. Then treat it with a good quality line dressing before putting it back on the reel. I run it through my fingers as I wind it on to the reel. It removes the dust and excess dressing. When I'm away from home on a trip, I run my line through a wet washcloth and let it dry each night.