I have some criticism about the cost basis reported on brokerage websites. It isn't your out-of-pocket cost basis. It accounts for reinvested dividends. As a result, the gain/loss number might be a misleading color. The red loss number might make it look like the investment was a poor choice, but in fact you actually the investment grew in value.
Let's look at SWAGX, a aggregate bond index fund. My initial out-of-pocket investment was $1,000. After some time, it collected $4.17 dividend and was used to buy more shares of SWAGX. It's NAV also dropped in value during this time. The net effect of the interest and the NAV drop was +$0.06. The investment grew by 6 cents. It's good! But it's sidelined by this ominous red -$4.11 gain/loss number. These two numbers have contradictory feelings.
I realize the previous example is simple. I could have just written down in my notebook that my out-of-pocket expense was $1,000. Then I'd ignore whatever is in the gain/loss column. I'd take the market value minus the $1,000 to get my investment growth. However, I have other funds that are much more complicated: dozens of lots bought at different NAV price points. In these complicated cases, how do you personally keep track of the growth of the investment above your out-of-pocket cost basis? It's really hard going into my history and adding up all those numbers. I just want a quick way to evaluate whether the investment grew or loss.