In SEGWIT transactions the witness data is excluded which makes the transaction occupy a smaller block space however in the legacy address the witness and script data are included increasing block space and transaction fees.my point here is how important is the witness data ? Is it less important that excluding it using SEGWIT will have insignificant effect on the transactions?
It's only excluded by nodes that don't support the soft-fork, Bitcoin nodes that upgraded has it in their blockchain, just "
Segregated".
So the answer to your question is: it's not important to pre-SegWit nodes since they read SegWit outputs as something else which doesn't require the witness data.
Read "
Backward Compatibility":
BIP-0141The regular byte is weighs 4 weight unit and the vbyte weigh just 1 weight unit.
It seems like you know meant "
non-witness" and "
witness" data.
Because you've used the term "
vbyte" for "
witness",
the sentence became incorrect since a transaction with 200 vByte would've been 200 Weight Units if it's true.