the point of the feature is to prevent sleeping cells ! the sgsn will “ping” the MS in the cell, in order to force the cell to be continuously “gprs awake”.
With the feature disabled, it’s normal that the sleeping cells increase. Otherwise it means the feature is useless 🙂
Now “why are cells sleeping”… this i don’t know. It’s more or less apparent in different vendors. I believe I read that E/ is doing this “ping” by default.