ADD ON CARD

Depends on the bank.

With add on card you can use offer again which you get with primary card. 

Here's the gameplay -

Banks like offering add-on cards because they are getting more business (through more usage / swipes) and are transferring the liability / risk on to the primary cardholder.

For customers, add-on cards are easier to get for family members rather than doing a fresh application. Also in the case of paid / annual fees cards, add-on card helps save/split those.

HDFC is infamous of offering add-on cards with same CC numbers. Thus, for online transaction OTPs go the primary cardholder's mobile phone. SBI, Citi and ICICI issue add-on CCs with different numbers and OTPs go to the add-on mobile phone.

Another advantage of add-on cards is that offers can be redeemed both on the primary and add-on card, most of the times. In rare cases, it is only limited to primary cardholder.

And it really depends on your use case. Examples -

Infinia waives off fees on spends of 8L/year. If you only have 5L/year expenses but your family member has 3L, you can take an add-on card for them and save on the annual fees.

Infinia/DCB offer airport lounge access to add-on cardholders. If you don't travel by flights but your family member does they can benefit.

Some banks force a savings account to get a CC. An add-on card can let you bypass that requirement.

Add On Card only good IF to whom you give it also has sense of using credit card in sensible manner.

I have seen cases with friends , relatives where wives, college going kids got addon cards and spent lavishly,  created huge Credit debt.

Will lounge access work for add on card members say axis my zone or fk axis?