For me CTL really just relates to my training volume, not necessarily my fitness. For example if I do a lot of high intensity interval training with proper recovery my CTL drops lower than if I do a load of high volume base. I just don't think TSS really combines intensity and volume equally. At least not for me. I need a lot more recovery from a 100 TSS intense interval session vs a 100 TSS base ride. So that tells me that they are not really equivalent levels of stress. So then ATL is also going to be misleading. But what I do get from tracking CTL/ATL/TSS is an idea of where I am during a specific training block. But if I change from one kind of training regime to another then CTL doesn't compare very well across the two different regimes. Right now my CTL is only 51, which is the lowest it's been all year, but my real world fitness is actually peaking. So I don't think the absolute CTL value is all that useful, but tracking changes in CTL/ATL during a consistent training block is fairly useful. What you can't say is that a CTL of 80 automatically means you are fitter than at CTL of 50. It only does if they are built on exactly the same kind of training regime. Otherwise it's apples vs oranges.