"AD on IP summary Address in Eigrp"

Is there always necessary to add an AD value (less than 90) while
configuring manual summarization in EIGRP by the command - ip
summary-address eigrp <AS no> <Ip addr> <Mask> <AD> or it is only required
when we are doing the manual summarization of same ip addresses on
different routers in order to avoid the reception of summary advertisement
of same address from different routers.

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