Pretty useful but not necessary in 90% of cases. Your highest rank tash is almost always enough to make a charm manageable pre PoP at least. You can squeeze in extra MR debuffs by carrying a few easy to acquire pieces of equipment to give to your pet. The two I always have on me are Rusty Spiked Shoulderpads and Adamantite Band/Silver Jacinth Wedding Ring. The big stand out exception I remember is the velium hunter in velks. Malo was a godsend there because the thing is resistant and absolutely destroys you on charm breaks if you've given it a weapon to backstab from the front.