I have been to Alfa store a few times but never to Makro. I would say they are similar. Can't compare prices as I went a year apart to each one and didn't write prices from Alfa. Alfa is closer to Kuta though and you don't have to buy in bulk.
The main things I bought at Macro were things for home. Buying toiletries there saves quite a bit compared to purchasing at home. Plus most of the things I bought were light and took up little room in my bag.
I bought Rupiah Sydney price
12 OralB toothbrushes 33.700 =$4.80 $36+
6 pkts cotton squares (for toner for face) 10.700=$1.50 $12
2 Pkt Panty liners (32) 10.000= $1.45 $4
3 Head + shoulders shampoo 30.700= $4.40 $14
Carton Cigs - Marlboro Light 62.000 =$8.90 ?
Vicks cough mixure 12.600= $1.80 $8?
Betadine antiseptic 30ml 11.500=$1.65 $8?
Jar Balsam heat rub small 1.500= 20c ?
Deodorant sticks
I also bought but at other places
Bodrex (paracetamol + codiene) 2.300 strip
Pandol cold and flu tablets 5.500 strip
Antiseptic cream 6.450
You can get canestan for 19.000= $2.70 (it's over $10 a tube here)
Vicks vapour rub 5.000
I usually have room in my bag so getting this stuff just saves a bit of money when I get home. It's things I need to buy anyway.
I also get some moisturizers, toners, mascara etc there. Watch out for the ones with whitening agents though.
Macro/alfa are great for stocking up at the beginning of your holiday for things like alcohol, soft drinks, water, nibblies etc. There is also a bakery at both. I saw a nice chocolate cake for 25.000 (looked like the mud cake you get from the cheesecake shop here). If you are having a birthday, they have birthday cakes but not sure if they were ordered. They have pastries etc also. At Macro they also have a seafood section. They had green prawns (large) for 75.000 a kilo.
Well worth a look.
Bring bags or you can buy large bags for 2.200rp.