Keyword dumping?

Hello,

I have just been reading online (not on this forum) about keyword ‘dumping’ in Amazon PPC campaigns and I’ve found a lot of different advice online suggesting you should keep the number of keywords in a single ad-group down to 100 or fewer. I understand the idea is to optimise by removing low-performing and potentially increasing bids of high-performing, but I dont understand the disadvantage in having lots of keywords. Some people were suggesting Amazon would randomly pick batches of 100 to show each week, but I didnt see any evidence of that. Also, lots of people suggest separating exact, broad and phrase into different ad groups but again i dont fully understand the reasons given i can filter by match type and adjust bids accordingly.

I have a manual product keyword campaign with 1000 keywords. This is because i have attempted to capture every variation/permutation of the search terms i expect. Is this bad? Would I be better just using phrase/broad match to basically do that on my behalf?

For a theoretical listing of a tshirt, available in different sizes and different colours, I have taken the approach to add keywords like:

1. tshirt blue large
2. tshirt blue medium
3. tshirt blue small
4. tshirt red large
5. tshirt red medium
6. tshirt red small
   etc.

And then I have added each permutation 3 times: once as exact (highest bid), once as phrase (medium bid), and once as broad (lowest bid). It didn’t take me long to hit 1000 keywords!

Any advice would be greatly appreciated. I guess if noone has any strong, evidence-based suggestions I can still just trial what I’m reading online, but I prefer not to follow things blindly and I haven’t yet read anything which fully explains why keyword ‘dumping’ is bad. I’m not using anywhere nearly my budget so it isn’t true for me that keyword dumping is exhausting my budget. I think i have probably 70% of keywords never getting any impressions, but whilst that may be unnecessary, surely thats not a disadvantage???

Thanks,
Adam