I pad Performance.

Using a VPN introduces an additional [small] protocol overhead, which are only likely to be noticeable when using a slow-speed/bandwidth-restricted network/internet connection - or a benchmarking App. When using a high-bandwidth internet connection, you are unlikely to notice an appreciable impact to device performance.

The additional processing of VPN traffic does add to processor loading - and again will lead to a marginal increase in battery consumption. Some VPN protocols are more efficient than others.

In summary, while you may note a marginal increase in battery consumption, it is unlikely to be significant.

well it can slow down the network traffic as all data would go from site to the vpn server and then to your device rather than from the site directly to your device.

if you don't know what vpn really is then you should read up on it before using it

Virtual private network - Wikipedia