As Kent Beck notes when discussing guard clauses in Implementation Patterns making a routine have a single entry and exit point ...

"was to prevent the confusion possible when jumping into and out of many locations in the same routine. It made good sense when applied to FORTRAN or assembly language programs written with lots of global data where even understanding which statements were executed was hard work ... with small methods and mostly local data, it is needlessly conservative."

I find a function written with guard clauses much easier to follow than one long nested bunch of if then else statements.