I like putting markers on data points in line graphs. Especially where a line is relatively flat, it makes it much easier to see and compare different data points on the graph. Over the years, I have cursed Excel's graphing tool on many occasions, but it was pretty easy to add and change the style and formatting of data point markers, so I was really surprised this was such an ordeal in Tableau as I was working on my Football Player Retention viz.
Clicking the color box in the Marks pane did pull up an option to add a marker, but it was just a small circle one. I then read in the Tableau forum that I really needed to add my measure to rows a second time and put that second pill on a dual axis - I'm pretty sure I did this by clicking the arrow in that second pill in the row. But this created other issues. I now had two vertical axis titles and two sets of tip tools showing up when I hovered over my graph.
Getting rid of the right hand axis title was a quick fix. I'm pretty sure I right clicked the axis then unselected Show Header. Let's hope I don't want that axis title again, because I can't figure out how to make it show up again.
The tip tools were more problematic. I ended up going to "All" in the Marks pane and clicking on the Tool Tip square. This allowed me to edit what I wanted in the tool tip. However, I was still stuck with the second tool tip that appeared when I hovered over just the line - it was missing one of the elements, so I didn't want it to show. What finally worked was going to the section of the Marks pane with the line, clicking on the Tool Tips square and deleting everything in the edit area.
I haven't gone into having different markers for the various lines - that's a battle for another day.