A sink tip line will sink your floating flies. That's it's purpose.

If you fish still waters for warm water fish, you really should look into a full sinking line.

For bass/bluegills/crappie/catfish being able to get down to that eight to fifteen foot depth range will improve your catches significantly.

To start, get the fastest sinking line your rod can throw. Use the countdown method to find the fish.

If you want the opportunity to fish topwater as well as use a sinking line, you will need two rods (otherwise you will be changing spools/reels every time you want to throw a popper or such, then changing back when you want to fish deep). Good excuse to buy another rod and reel.

Remember that you can't really 'pick up' a length of sinking line. To use it effectively, you'll want to retrieve it all the way in, then recast.

After you get used to a fast sinking line, you may want to add other sink rates. An intermediate line is great for fishing Clousers in shallow water, and a medium sink, someplace in the 4-5 inches/second range, is great for those four to eight foot depths in the spring and fall.

I've gotten to where I carry a number of rods rigged for different presentations, matching the sink rates of the lines to different depths and flies. But I've 'collected' rods and reels for years and have them to spare....

Good Luck!