Is a simple syrup necessary on your cake??

How long does the simple syrup keep for??

And does it make your cake soggy??

No, it's not necessary. It depends on your recipe. If it's a flavor you want to incorporate into the cake then I would think yes. If your trying to make the cake more moist maybe try a different recipe. Not sure how long it keeps. It shouldn't make the cake soggy, the idea is to lightly drizzle it don't soak the cake in it.

.......Is a simple syrup necessary on your cake?? .........
No. It might depend on the recipe you are using but if the cake is overbaked nothing will restore the flavor or moisture.

....How long does the simple syrup keep for?? .....
I have kept some in the frig for up to a month

........And does it make your cake soggy??.......
Not if you brush it on. If you pour it on yes, it probably will.