Depends how rotten the wood is.

Your wood is basically grain (the hard stuff) and pith (the stuff in between
the grain). If you pith is rotted away but you've got some grain left, the
resin in the Git Rot will replace the missing pith.

Whenb the wood is so darn rotten that it's missing completely, it's time to go
get wood, not Git Rot.

Is it a substitute for a proper repair? Usually not. Will it allow you to "get
by" a while longer in marginal conditon? Often it will.