user64788: So one priv key express uncompressed and compressed pub key.
Does the latest Bitcoin Core client accepts importing it to express uncompressed address? or it automatically express compressed address?
I have not noticed related parameter for compression options in getnewaddress and importprivkey.
Is this because compressed addresses helps reduce transaction size?

user52021: You can import an old uncompressed key. It'll work fine.  Getnewaddress always uses scripts with 'compressed' keys now.  BIP-143 (segwit) style inputs also require compression.
The smaller key format results in smaller transactions, and where it's required and not just optional also simpler code.

64788: <p>So one priv key express uncompressed and compressed pub key.</p>

<p>Does the latest Bitcoin Core client accepts importing it to express uncompressed address? or it automatically express compressed address?</p>

<p>I have not noticed related parameter for compression options in getnewaddress and importprivkey.</p>

<p>Is this because compressed addresses helps reduce transaction size?</p>
 52021: <p>You can import an old uncompressed key. It'll work fine.  Getnewaddress always uses scripts with 'compressed' keys now.  BIP-143 (segwit) style inputs also require compression.</p>

<p>The smaller key format results in smaller transactions, and where it's required and not just optional also simpler code.</p>
