I have some queries.
1.Mention what is the benefit of applying Connect Patches in Magento? 2.Why all patches are not implemented ? 3.How to check whether it is correctly installed or not ? 4.Is there any issue if magento site dont have patches?
Re your second question:
2.Why all patches are not implemented?
The newest Magento version includes all patches.
Magento 2.1.0 and 2.0.8
Magento 1 ver 18.104.22.168 - Added Feb 23, 2016
Includes patches: SUPEE-5344, SUPEE-5994, SUPEE-6237, SUPEE-6285, SUPEE-6482, SUPEE-6788, SUPEE-7616, SUPEE-7405, SUPEE-7405 v1.1