What difference is there between Whatsapp & Google contacts as long as both sync on same account

[a cooperator]

Hi Everyone!
First of all, I don't know if you're going to understand me or not. But, simply, why there are Whatsapp contacts and Google Contacts as long as Whatsapp contacts are affiliated to the same numbers of a persons in the contact address. Even if I've many Whatsapp account registered with the different numbers, then no need to have Whatsapp contacts separated from the Google contacts saved on the same Google account linked with the Whatsapp number.

I added my Google account which is synchronised with the stuff of my phone.
Since adding any new contacts to my phone storage are not synchronised with my Google contact via the google account, then I am using Google Contact app to manually move any new contacts added onto my cellphone storage.

While editing a contact in an address book, I see that I can separate the Whatsapp from the Google contact. So, I will have a Whatsapp contact and Google Contact. So, Why do I see 'separate' a Whatsapp contact from the reset of the details of the same contact in the address book although the same number is used for communicating via phone or whatsapp?

I.e. why I need to have Whatsapp contacts, Google contacts as long as all are synchronized on the same Google account linked with Google Contacts. So, once I added my Google account on my device, I've gotten my contacts added there regardless of there is whatsapp application is installed or not.
It is really confused to have Whatsapp contacts and Google contacts filtered or separated from Google contacts on the same device(cellphone) as long as person-to-person conversations can be be done at persons' numbers saved in a contact in my address book or through her/his Whatsapp (if there is Whatsapp installed on my cellphone, and that person contact to be added have a Whatsapp registered with her/his number). I.e. no need to have Whatsapp contact separated as long as the same number, itself, is Whatsapp if registered with)?
Why I need to filter contacts to be displayed as Whatsapp contacts, the Added Google account contacts as long as they are backed up and synchronised onto the same Google Account.

 

[lvt]

I think it's because WhatsApp is a cross-platforms app. If you are using Line or Viber app they also have their own Contact list. That way when you transfer your account to other devices you don't have to start from scratch.

 

[a cooperator]

I think it's because WhatsApp is a cross-platforms app. If you are using Line or Viber app they also have their own Contact list. That way when you transfer your account to other devices you don't have to start from scratch.

Thanks a lot,
First of all,
I am really using 'Google Contact app' to move any new contacts added to my storage phone since sync my Google account won't help sync any new preservation in "mobile phone contacts". However, syncing my Google account on my mobile phone only helps sync what happens on online Google contacts.
So, all my cellphone contacts are manfully backed up/ moved to my Google account - online Google contacts- through the Google contacts desktop client app, installed on my cellphone.
After that, they were moved to my online Google contacts, then they can be shown on any cellphone\device is synchronized with my same Google account.
Next, any changes in the contacts happening on any devices will be reflected on all other devices, and vise versa, any changes on online Google contacts will be reflect on all contacts on devices as long as my Google account is still synced with all devices.
So, I don't have any phone mobile contacts saved.
Once my Google account got removed from any of those devices or cellphones, then all contacts have been stopped syncing, and no longer available to be shown on my cellphone.

My questions are as follows:
1- Having said ' Line or Viber app', you think it is working with the same mechanism Google Contacts works.
2- I think I will need only to sync a Google account with my devices, so all Google contacts will be synced on all my devices. Why I see sync 'WhatsApp" under accounts in the settings of a cellphone as long as syncing 'Google account' will already be syncing contacts between my devices and Google account. So, even if I have a WhatsApp account, then the same Google contacts will be considered as WhatsApp contacts if their owners registered with WhatsApp. I hope you understand me here to eliminate the ambiguity of having WhatsApp contacts and Google Contacts.