A general rule is that your code should have only one way to return. But general rules are often broken.
"Single Entry, Single Exit" is a rule described by Dijkstra in his writings on Structured Programming. I don't think it really applies quite so strongly today, not because it isn't relevant or good advice, but because programming languages typically used today don't have the features that he was warning against using.
Single Entry meant that functions should not have multiple entry points. This was a feature provided by FORTRAN and COBOL allowing a function to pepper alternate entry points within a single routine. Single Exit meant that a function should only return to a single place, the statement immediately following the call; the behaviour Dijsktra was warning against was the at the time common practice that a FORTRAN program would actually return to an alternate location other than the statement after the one that the function was called to indicate an error condition.
These were not bad language designs, but at the time of their conception they were necessary for software to be performant on the hardware of the day, and, particularly for FORTRAN, competitive performance-wise with Assembly programming.
