Just to add to that, your example would be even worse if you didn't have the macros at the beginning: F_{1\mathrm{l}} &= F_{2\mathrm{r}} + F_{2\mathrm{l}}

Just to add to that, your example would be even worse if you didn't have the macros at the beginning: F_{1\mathrm{l}} &= F_{2\mathrm{r}} + F_{2\mathrm{l}} \exp (i\,k_2 L) + F_{\mathrm{Br}} + F_{\mathrm{Bl}} \exp(i\,k_\mathrm{B} L) ... The obvious objection is that of course most people do use macros. But that's the point: every LaTeX document ends up being its own impenetrable language.