If you have been working for some years, you should have a rather significant amount of money in your CPF Special Account.
The interest is high enough to make it unattractive to some people to use the SA money for investments. Fund houses and unit trust marketers may think otherwise, but it’s not hard to see why they are biased.
Another reason, though less compelling, is that your CPF SA serves as an approximate proxy for the total income you have earned so far.
By looking at your CPF SA balance, you can roughly* have an idea of the total income you have made in your working life thus far. You can use it as yet another way to compare your earnings. (This is of course assuming that you did not use your SA for investments under CPFIS-SA.)
On the other hand, comparing the Ordinary Account is harder because most people use part or all of the OA money for their HDB or private property loan payments.
*Factors affecting your CPF SA balance include: the number of years you have worked, the bonuses you have received, and whether your wages exceed the contribution limits.