Unhappy [Q] Android Cache Cleaning Issue

Hi guys

My phone is Micromax A63 with 2 GB internal memory and 512 MB Ram (Not rooted), I am using 360 mobile safe app. Recently i noticed some strange activities in my phone. At once it showed 250MB Internal memory is free. So i thought cleaning Cache incluiding system cache may further increase the Internal memory. I used 360 mobile safe to clean cache and system. It showed 170MB cleaned. I returned to the apps section and i found that only 125MB Internal memory is left !!! Memory decreased instead increase.

Is anybody know why it happens ?
Is it good keeping cache ?

I hope someone will solve my problem.