Why low bodyfat before a cycle ?

[MR-FQ320]

Hi there, iv read a hell of a lot of threads and posts on here, and held off starting a cycle of test e due to a lot posts saying you should not start until you have your bodyfat at a acceptable level,

So my question is this : why ? And what would be an acceptable level ?

[Shadeed]

to avoid estrogen related sides, i would say 10-15% is okay...